SMPS for vacuum tube power amplifiers.(status: back at it) - Page 1
Forum section: electronics / projects

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 28, 2019, 09:39:37 pm
content: Hello. I designed a switchmode PSU for tube amplifiers. The PSU is capable delivering upt to 70W of power and runs of 10 to 30VDC on the input. The output can be adjust to anywhere from 200V up to whatever your filtercap is rated for (450V). This was originally an idea of mine to switch out a really expensive transformer for the High voltage which would be nowhere near regulated and really heavy. The Powersupply has its advantages and its problems but those seem to be so far easy fixes. The big deal is, would anyone be even slightly interested in such a supply. I know that SMPS were frowned upon because of their noise, while my supply generates 0 audiable noise at the speakear even when looking at it with a scope.I originally intended it for my school project for a Tube amplifier. 20W RMS Mullard amplifier more specifically. Workse great no hiss nothing, I also posted the same question on a site called DIY Audio and one of the guys messaged me if it would be possible to power it with basically line voltages. My design has some problems and those would be fixed right away if working with line voltage, but I kept myself away from such a job because I simply dont feel comfortable enought to work arround line voltages.Its basically a Flyback converter that stepts the voltage up to 450V with a lot of power to back it up.Little bit bout me- Im a student and I just turned 17 last week and I basically consider myself as a home grade enginerd. Im into mostly analog stuff, high power regulators semiconductor amplifiers and many other things. Before you askt, the entire high voltage power supply was created by me. THere is no existing schematic for such a powerfull flyback converter from said input voltages to the said output voltagesI wonder if it is worth it a all to continue the developement of the supply at all.Btw im not a native speaking so I apologise for any grammar mistakes I made.Thanks

author: Benta
author_rank: Super Contributor
timestamp: March 28, 2019, 09:51:54 pm
content: First, I applaud someone really enthusiastic about electronics at 17. Keep it up!About your current project, I have my doubts. Tube enthusiasts tend to be purists and like big transformers etc. I don't think you'll find customers in that area.

author: TimNJ
author_rank: Super Contributor
timestamp: March 28, 2019, 10:37:41 pm
content: Most "tube enthusiasts" are perfectly content in the year 1955. It's audio, so there's a lot of ~feelings~ involved, as we know. So, you're unlikely to have much appeal with that crowd.That said, an SMPS would allow you to cut down on size, weight, and maybe cost of a tube amplifier. Could be an interesting design challenge to see how small you can go.I'm not entirely sure how you deal with the output transformer, though.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 28, 2019, 10:56:58 pm
content: Quote from: TimNJ on March 28, 2019, 10:37:41 pmThe output transformer has to stay- its there to convert the tubes high impedance to low impedance that matches the speakers. Its a necessity BUT getting the power transformer out of the way it basically halfs the total weight of the amp with some advantages as of powering it from 12V batteries, cars, and more, also its tightly regulated and it has absolutely no noise whatsoever, and maybe even improved efficiency, but converting to 450V from 12VDC aint a an effective process. But I had a rather intresting requiest by one individual asking me to make a line voltage version. It would be much simpler in terms of managing losses and heat problems since more power but less current is involved. I had to use a IGBT for switching the transformer since a regular MOSFET has a body diode which creates unwated effects in the circuit. I know that people have feelings for the good ol transformers, and I dont blame them, go linear go quiet. But these days technology can achieve same, and the line being noisy aswell the transformers are not so different from my supply I designed. Im hoping to draw some more poeple into this, currently im recovering from the financial loss of making the tube amplifier itself and getting the HV PSU done. Once Im up again Im going to work further on the PSU. It will work of of proper mains rated from 90VAC to 265VAC with a power of abou 100W thats my goal to reach and up to 1kV of voltage. I dont have really the proper tes equipment for that except a old VTVM (vacuum tube voltmeter) I love dearly but the filament current source "barretor" seems to be not in the best shape at all. And it seems to soon require a simconductor fix. However it goes to 1kV full scale so no problems there. I just hope this project aint my last one xD. The 1kV output would be really catching for tube RF transmitters.I know the stigma arround anything else than true linear transformers, but at some point..someone has to come up with something that might be worth a shot. I could not find ANY comercial device that could provide this amounth of power or anything close. Not even an IC that do the work so I had to design my own SMPS controller based on the literature of MAXIM integrated and making the ctriangle gen and PWM gen and error amp so experimental purposes. As of now the GA3459 switching transformer is rated for 56kHz switching. The line voltage transformer could go even higher up to 100kHz would really improve noise basically eleminating even the electrical noise I can see with my old HP digital scope with a divider probe amd the fluctuation is about 1V pulses. Again nothing noticeable at that voltage. I also have a RLC filter there fo it does a real good job at filtering (10R series 470uH series and 100uF in paralel. The previous stge has only a 8uF filtercap after the diode and a very big fat 630V SMD cap biggest one I have ever seen in my life.). If anyone would be interest I could upload a video on youtube abou this. But the biggest problem im afraid of of the people to really hold onto those tranformers like even if my solution fits into 50 dollars and thats well within the manufacturing cost the engineering cost and the component cost.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 28, 2019, 11:03:54 pm
content: Quote from: Benta on March 28, 2019, 09:51:54 pmWell hey thank you its been my passion ever since I was 8- from blowing stuff up into making making functional custom made products for special use and other things. I consider myself as a ENGINERDYeah I have the same fear. Regardless I think people woul reconsider buying a 150 dollar transformer shipping not included or a 50 dollar same solution just lighter and not traditional as we could say. More versatile lighter maybe even more effective But I havent done math arround efficiency yet. I wanted to get it working for the competiton but it did not work out the way it was suposed to- the competition. You know how it works.. That one old guy saw me at the cross country competition this year totally crushing the school he brought hes students from and he probably made damn sure to not even let me compete xD. Ahwell screw competitions those aint bring money only pets my ego. But yeah it would have been the 6th competiton this year. Still got two more to go.About trannsformers- one would have to be left and thats the output transformer. It is necessary for a tube amplifier because vacujm tubes are high impedance devices- they cannot drive speakers directly like transistors. Tubes need a way of transforming high impedance to low impedance that matches the speakers there is the big fat output audio tranformer for.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 29, 2019, 03:37:31 am
content: Cool!I did a few things like that at the same age, too, although I don't remember making an SMPS for that purpose as I always had mains transformers handy, and didn't need battery or mobile operation.Here's an example experiment, merely a multivibrator, switch and rectifier. Probably circa 2001 or so:I didn't have any schottky diodes handy at the time, not in that voltage anyway (indeed, 600V and higher parts -- SiC schottky -- were introduced since then!), so I actually used a tube for the rectification itself, too. 17CT3 was another I played with, convenient to use with the 15V bench supply I had at the time.As rectifiers go, tubes are actually pretty impressive, if you can ignore the pesky heater power requirement that is.Like schottky diodes, tubes have essentially no recovery losses. Unlike schottky, they don't have an exaggerated nonlinear capacitance response. They also have no junction voltage drop (an advantage of the heated cathode, which actually has a negative zero-offset current -- yes, it generates electrical power from a temperature difference: it's a heat engine, if an extremely poor one!), which makes them better signal diodes than any semiconductor, for sufficiently small signals (under 200mV say). Finally, they have massive internal resistance, due to the voltage drop of all that vacuum. And, again, a massive heater just sitting there cooking away.Since then, I've made many SMPSs. Here's a dual output module for hybrid* supply duty:*As in, a low voltage linear supply powering a switching supply, as opposed to an offline switcher.I've got one of these in my ever-evolving hand built Theremin,https://www.seventransistorlabs.com/Images/Theremin7.jpgin the shielded module on the right.It's powered by a 15V 1A wall wart, hence the hybrid title.There are some small differences from the above circuit, like joint regulation (a feedback resistor from 6.3V as well as 100V, to the TL431; regulating just 100V prevents it from starting up because the 6.3V rail browns out from the cold heater load).Note the juxtaposition of a switching supply in a radio frequency project -- a Theremin is very sensitive to RF noise around it, acting like an electromagnetic microphone at its operating frequency. This is why the power supply is shielded, and it helps that it is common ground, not isolated -- when isolation is required (like an offline supply), filtering must be very carefully implemented, otherwise it just leaks out everywhere. Understanding how to do this, is one of the most important and rewarding lessons of switching supply design!Cheers,Tim

author: TERRA Operative
author_rank: Super Contributor
timestamp: March 29, 2019, 04:21:16 am
content: I am definitely interested, myself and a musician friend have just been talking about this exact subject.He wants to build himself a guitar amp that is as small and lightweight as possible for taking to gigs. (He used to build guitar amps as a side business years ago).I'll be following along for sure.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 09:30:43 pm
content: Quote from: TERRA Operative on March 29, 2019, 04:21:16 amGood to know. Considering people want to see such a power supply even on the audio forum, I made the decision to go with the developement, leave the 10 to 30V input to 450V converter and go for the mains powered version.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 09:32:02 pm
content: Quote from: T3sl4co1l on March 29, 2019, 03:37:31 amThats looks interesting- but it seems not to provide almost just very minimal power if any at all. Youre right about tube diodes. In fact my VTVM (vacuum tube voltmeter) uses a pair for rectifying the AC voltage so it can provide a reading. I probably have one of the rarest VTVms ever existing. Back in the 50s Tesla in czechoslovakia was the main manufacturer for really thee entire soviet european block. So this very rare voltmeter does not even have a schemati available really on the internet xD Not even the manual. Its called the Tesla BM388E (not the round style but the rectangular big box style). It was quite common to use batteries back in the days for ohms measurements this one has a tap o its transformer for just that. So yeah very advanced VTVM. Regulated heatersupply and such- lotsa fun restoring. The only thing im sad about is that the scale is getting crusty and the paint wants to flake of badly. The one I use is in relatively good condition but the other one I also have has its scale almost unreadable.Back to the subject- I actually use fast recovery rectifiers instead of shottky diodes simply because locallly theyre not available for me and fast recovery rectifiers considering the high voltage and low current flowing trought its not an issue.And oh boi that shielding tho. Lotsa PCB material there xD.So yeah and considering people actually want to see a line powered version, well heck why not I ordered the switching transformer today and lets get going. I just hope it wont be my last project xD. SO the thing by ma estimation will be capable to go up to 100W no problems. This really scares me cause I always try to keep myself away from line powered projects. I mean no doubt that the 12 to 450V converter is nowhere near a safe device. But I at least know that there aint anything before that can supply A LOT MORE. But over the years I think its finally time to overcome that fear of running away from line voltages. And its really noticeable by looking at the eficiency of the 12V in version. By having it runing on a higher input voltage, it will allow me to double the power safely and make losses less of a problem.So yeah, Im in it now. Going further to make this a really good option. So far the whole thing has been designed on a single sided board and THT components. The shear PCB size can be smaller as soon as ill use SMD components and probably go for the TL494 chip instead of making the whole thing myself. Also by going double sided it will help a lot. Im going to attach some images for you to look at.(pics will be in a separate post)

author: TimNJ
author_rank: Super Contributor
timestamp: March 29, 2019, 09:57:20 pm
content: I work on offline AC-DC SMPSs all day. Shocked myself many times, but haven't been seriously hurt. Classic electrician's rule is to "keep one hand in your pocket". That's a good rule of thumb here too. Try to work with just one hand, especially when the circuit is powered up.Of course, there are many other preventative measures to prevent yourself from getting cooked, but that's a good start.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 29, 2019, 10:07:00 pm
content: How is a device intrinsically unsafe?Energized, stick it up your bum? Not very safe, no, wouldn't recommend that.Energized, under a cover, or inside an insulated box, connected with insulated terminals, connectors, whatever -- not a problem.We handle hundreds of volts on a daily basis -- to varying degrees of safety mind, but mains outlets are hardly mass murders. YMMV by country -- US plugs being notorious (you can easily touch the prongs when partially inserted), but 120V also arguably not being very dangerous by itself. UK and AUS plugs being safer, with the metal bit on the end, atop an insulated shank, and preferably with the outlets having shutters that retract when a ground prong is inserted. And arguably being more justified in the increased cost, at the higher voltage.All a matter of safe practice. And where possible, safe hardware and tools. You don't have to get obnoxious with rubber gloves and face shields and finger guards all over -- after all, the most unsafe protocol is the one that doesn't get followed! -- but there are some very reasonable and affordable steps that can be taken to improve confidence in things.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 10:08:56 pm
content: Quote from: TimNJ on March 29, 2019, 09:57:20 pmI know that rule very well. I did get bit quite a bit of times and usually it was because of my stupidity. I did not expect the inductor to zap me but the voltage was so hight it penetrated the isolation. Something that is so obvious, but for some reason im still an idiot sometimes. Nothing to major tho. Since that day I use speacial isolated gloves if I really want to look at stuff and handle electronics while turned on, I use covered probes right to the tip. And no the gloves wont be penetrated by the sharp leads sticking out the bottom of the PCB. And me having dry hands as the sands of sahara is also a bonus.Learned my lesson lol. But the question still remains. I see a lot of feedback circuits, but Im afraid I dont get their function(how does it work exactly). I mainly look at the TL431 feedback loop with an opto. So far doing research about the regulation.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 10:22:26 pm
content: Quote from: T3sl4co1l on March 29, 2019, 10:07:00 pmUnsafe..well there aint nothing safe on 450V of DC with abou 60W of power backing it, no matter if its generated from 12V or 240V. The thing is I dont like working arround mains because ITS UNFORGIVING. You do a mistake you pay for it. Doesnt have to be about touching live stuff. Even simple mistakes can turn into disasters. The deal is I simply never was comfortable working arround those voltages. Maybe fixing powersupplies, its not a problem, but powering my own circuit with mains? Something I havent done yet and also I dont really "have the balls" to just turn it on. Sometimes shit can go haywire and I simply hate to risk anything.

author: Zero999
author_rank: Super Contributor
timestamp: March 29, 2019, 10:50:35 pm
content: Do away with the power transformer altogether and go with good old school hot chassis. This sounds dangerous, but it needn't be: the inputs and outputs can be coupled with transformers, with sufficient isolation for mains use.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 11:00:38 pm
content: Quote from: Zero999 on March 29, 2019, 10:50:35 pmNow that is what engineers were thinking of when they were designing all american 5 and 6 radios. Make the chassis hot or not- aint a good idea if you want the thing to be showed of not just working. And if you want a metal enclosure for the thing to make it premium looking.Now I would use a 3 wire plug anyways. But ground loops are still gona persist as an issue, and isolating the output from the input mains seems to logical since you dont want to spend tons of money for tranformers that will put your sound into the amplifier, afterall the catch of a tube amp is its high input impedance. Your solution, is not what Im after.

author: chris_leyson
author_rank: Super Contributor
timestamp: March 29, 2019, 11:17:41 pm
content: Well done, a really neat idea to get the weight downQuoteKnow what you mean. If I'm powering up a small off line 15W flyback design for the first time I use a small 24V to 500V flyback set to something like 325VDC and drive it from a bench supply limited to < 50W. At least that way there are no fireworks and breakers don't get tripped if shit does go haywire.One tip, put bleed resistors across the HV bulk storage caps and maybe a small neon indicator lamp as well. Simple reason is that if my off line flyback doesn't start up for whatever reason then there is nothing to discharge the bulk storage cap, apart from me and that is usually followed by an expletive. Always double check things and if in doubt just put a meter across anything that could be hot, play safe and enjoy.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 11:24:52 pm
content: Quote from: chris_leyson on March 29, 2019, 11:17:41 pmYeah thanks. Im planning to series 2x450V caps so the bleeders will be the balancing resistors themselves. The reason why I want to series them is to raise the voltage capability. Running a 450V single cap at that voltage can be little too close to the danger zone. If something goes oh shoot and the voltage shoots up into the sky, fireworks are expected..or at least a mist maker.

author: chris_leyson
author_rank: Super Contributor
timestamp: March 29, 2019, 11:31:54 pm
content: QuoteThat reminds me, I've been looking for a small HV transformer to retrofit to a old DAC90 receiver, two reasons, it's safe and I get rid of the hot dropper resistors. Haven't found anything that will fit yet.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 29, 2019, 11:37:06 pm
content: On the left side is the PCB of the tube amplifier. On the right is the HV converter.Just a showoff of the working 10-30Vin converter module

author: chris_leyson
author_rank: Super Contributor
timestamp: March 29, 2019, 11:40:56 pm
content: Nice

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 12:05:59 am
content: Heres the finished thing. Only the bottom PCB view for the SMPS. .

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 12:09:25 am
content: And some tube goodness. Warm orange glow with some blue powdery accent to it on the inside of the power pentodes.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 12:10:58 am
content: Heres another look at one of the power pentodes.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 12:13:04 am
content: And the last one.

author: Zero999
author_rank: Super Contributor
timestamp: March 30, 2019, 08:49:01 am
content: Quote from: SK_Caterpilar_SK on March 29, 2019, 11:00:38 pmIf input impedance is an issue, you could also use a low power pre-amplifier before the transformer, which would only need a small power transformer. Another possibility is to have a differential input stage for the valve amplif and couple the signal via Y-rated capacitors, which are safe to connect between the mains and exposed metalwork or a low voltage signal.I knew you wouldn't like my suggestion, but that was the point. I personally like your project, but as mentioned above, many thermionic purists won't. The fact that it sounds the same and the oscilloscope output is identical doesn't matter. It's phycological. If I told you it's possible to use digital signal processing to make an amplifier with exactly the same characteristics as a one with glowing filaments, would you be interested? Probably not. Many people like old technology. This is no different to steam enthusiasts vs those working on cutting edge electric locomotives.

author: Circlotron
author_rank: Super Contributor
timestamp: March 30, 2019, 09:57:02 am
content: Quote from: SK_Caterpilar_SK on March 30, 2019, 12:10:58 am6CA7 / EL34. Mmm...

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 06:51:42 pm
content: Quote from: Zero999 on March 30, 2019, 08:49:01 amAdded complexity. The preamplifier stage is not necessary and adds probably a lot more distortion than desired.I know it is possible to use digital processing to replicate the characteristics of a tube amplifier no doubt. But it aint the real thing, aint the visual appeal. I however did design a lot of chip/transistor amplifiers so I know myself that tubes are basically long obsolete and transistors are what it is todays and class D amplifier achieveving the same sound quality as any AB or even class A amps can get with the power rating of a D amp. The point wasnt really about the tube amplifier itself. Its more like a showpiece. But HVDC can be usefull in a lot of applications, HIFI guys are surely not gona agree but some quitar guys want a portable solution for tube amps and really replacing the transformer by this solution would basically half the weight of the thing. The HVDC supply does not have to be in a audio specific application. Transmitters use high voltage, and many other devices.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: March 30, 2019, 07:01:59 pm
content: Quote from: Circlotron on March 30, 2019, 09:57:02 amYes correct but its the EL-34L. The thing is made universal so it can use 6L6s, KT88 and such oktal power pentodes. The real advantage that would be given is by the KT88. You can upp the voltage on the anodes and get more power out of the thing.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 05, 2019, 09:03:51 pm
content: So over at the other forum people relly harrased me for wanting to make my own HV converter. Those people treated my work as a copy and paste, and were pushing their shitty chinese crap sinchronous inverters. Those converters do require quite the modifications to work as intended, but those supplies cant achieve what mine can, for example just directly connect to the output and call it a day instead of screwing arround with bs LCLCLCLCLCLCLCLCLCLCLCLCLCLCLCLCLCLC filters... cause the end of the day you end up with no power and thats basically geetting you nowhere. Also it gets no output regulation so in order to achieve your voltage you got to make a doubler for it. While mine just goes directly from the transformer to the diode and a cap and done. No aditional filtering required-small light simple. But considering the really crap response from those guys, I might just give up entire tube amp project and leave it as is. Afterall, who am I to create something new, a 17 year old student? Must be dumb as shit. I should just go get drunk all day night like my other classmates do and everyone in my age category. So yeah I give up. Its just anothersituation.

author: daedalux
author_rank: Contributor
timestamp: April 05, 2019, 09:52:39 pm
content: Never give up, just aim what you want to do in the good direction.What I wanted to warn you is that with the voltages and kind of equipment you are working with you should setup a isolation transformer for power, fuses and a 15mA residual current breaker that you'll set in the isolated zone, if you can't find one at least put a 30mA one that you'll find anywhere. I'm talking about your test set not what you design. This is very useful and needed for mains work, the transformer is usually multitapped which is useful and the breaker and fuses protect not only you but your test gigs and the parts you are working with.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 05, 2019, 10:19:39 pm
content: Quote from: daedalux on April 05, 2019, 09:52:39 pmMy bench is isolated and has that breaker..I thought of that little earlier, not cheap to get that residual breaker but I have it. The bench has its own breaker, and right at the bench there are two more low amp quick breakers one is for the variac. and the variac on the secondary side of the isolating transformer is wired trought the GFCI or whats it called. The isolation transformer is not multitapped, I had it made specifically for me on order. I did not need multi taps because why would I and the voltage arround here does not fluctuate. Living right next to the transformer station. My equipment is old id say very retro, for high voltage measurements I use a VTVM, you cant just about destroy one of those. All other measurements were done with my OWON multimeter but the turning knob is dodgy and it falied and it was brand new. So now I use my old nixie bench meter, works good, im happy with it, just a little space consuming but very nicely readable.But I might just not continue with the project I wanted to do, because of the negative feedback I got.

author: TERRA Operative
author_rank: Super Contributor
timestamp: April 06, 2019, 01:52:01 am
content: Nah, forget the haters, you have my interest and support.I am planning on doing the sxact same thing as a friend wants to make a lightweight, ultra portable guitar amp for taking to gigs.A heavy traditional amp is a bit hard to take on the Tokyo subway..... small and light is the key.So far, I plan to build two supplies, one HV PSU and one filament PSU, so it is more modular for reuse in other projects.I was thinking of adding a status output from the filament PSU that would go high once the filaments warmed up (current monitoring, time limit e5c) which would feed into an input on the HV PSU to only bring it online when the tubes are ready.This will also allow for the usual 'standby' switch you se on a lot of amps to be able to be used still.I'm just at the concept stage of my project, so I'm just starting my design at the moment.Keep at it, and don't let the haters get you down.

author: schmitt trigger
author_rank: Super Contributor
timestamp: April 08, 2019, 04:59:08 pm
content: @SK_Caterpillar_SKHaters will always hate. Most so if they are shielded from you by the web's anonymity. Don't pay attention to them.I once got flamed big time because I dared to publish the design of a switchingfilamentregulator! Calling me ignorant was the tamest insult I received.Your project looks very nice to me. Keep on experimenting, and be sure continue to post your results here.The only suggestion I would provide you, is that after thoroughly debugging them, clean them very well with IPA and then proceed with a spray-on acrylic conformal coat.That will prevent pesky humidity and dust from depositing across traces and creating leakage paths.

author: Circlotron
author_rank: Super Contributor
timestamp: April 08, 2019, 09:59:20 pm
content: SK_Caterpillar_SK,We actually understand what you are doingWe are with you all the wayThe opinions of people that have no understanding of what you are doing are worthless.

author: theworldbuilder
author_rank: Regular Contributor
timestamp: April 13, 2019, 01:58:20 pm
content: Hey SK_Caterpillar_SK,Just wanted to say that I'd be really interested in seeing this project progress.I'd definitely be interested in a smps for tube applications.I've been tinkering with my own SMPS for tubes for the same reason; I can't afford power transformers. But I've only ever built low power MC34063 based supplies which have tons of audio level buzz.I'd love to see what you've come up with so far and to see you develop this into a fully functional system! Keep it up!Never mind the audio snobs on the other board. I understand their wish to keep it transformer only, but it's just not practical. It's too expensive as you said.

author: Doctorandus_P
author_rank: Super Contributor
timestamp: April 13, 2019, 07:54:09 pm
content: If you are intesting with non-mainstream audio amplifiers then consider a voltage to current conveyor instead of a voltage amplifier.For more background info, read:

author: strawberry
author_rank: Super Contributor
timestamp: April 14, 2019, 09:37:07 am
content: LLC SMPS topology is the way to go in audio . you can find this kinda power supply on ebay aliexpress

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 14, 2019, 07:52:07 pm
content: Quote from: theworldbuilder on April 13, 2019, 01:58:20 pmProgress so far:The noise is caused by the filament heater supply being a crappy chinese PSU. I bought a 5V 8A supply that I modified the feedback to give 6,3V exactly, and some movearround. The entire thing is a Flyback supply. Its putting out 56W at the voltage shown (measured the anode current round about 130mA). The switching transformer for the mains version arrived but I dont know if I will ever use it. I hit so many roadblocks and solved one by other and so far the biggest problem is isolating the output from the input because you dont want mains refferenced output which ground can be either live or not. A second less of a problem is having ground loops. But the main concern is safety which I cannot reach currently. I need to figure out how to isolate the ouput voltage with a opto isolator from the input, and also figure out how am I going to power the TL494 on the mains side, so far I have came up with a capacitive dropper, would work but not ideal. The biggest thing slowing me down right now is the isolation, a problem that would truly need help with someone who knows how that stuff actually works.Yet still I get told to buy some ebay powersupplies just as on the other forum .

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 18, 2019, 10:05:00 pm
content: So here is my problem. Opto feedback for the TL494. Really the only issue is how do I choose the values for the components. The original values are for 5Voutput voltage. I need it to work in the range of 400 to about 630V. Or I can just have them a fixed a fixed value and solder the components accordingly for the voltages. I would really appreaciate if someone would rather show me a way how to choose these values instead of just giving me the values, if someone could tell me what values to use.My idea was to simply lift the entire FB circuit with a resistor, so instead of grounding it directly I would put a resistor where the ground was originally and lift that entire circuit above ground. I just dont have an idea if that would work, and the most criticall of all is that its best to not load the output but very lightly. Small mA currents in a 5V supply dont matter but 1mA at 500V is HALF A WATT. Not like its a big deal considering the output power of the circuit but its there just generating heat.Edit- the pics are fixed yes I noticed sorry my mistake

author: TimNJ
author_rank: Super Contributor
timestamp: April 18, 2019, 10:55:54 pm
content: Popular ways to get a low-voltage Vcc rail for powering your primary side ICs are...1.) Add another winding to your transformer. Usually called 'aux winding' or similar. You'll still need some sort of "bootstrap" supply to get the thing up at startup.2.) Use a small offline switcher. Power Integrations makes controllers with integrated MOSFETs. Those are nice.Regarding the output error amplifier. There are rigorous ways to determine those values, and not-so-rigorous ways to determine them. Ideally, you'd like to know the gain/phase response of your entire system. Then, you apply compensation to your feedback network to ensure that the system is unconditionally stable, under all conditions. You can look up feedback network compensation with TL431.You can basically change:1.) DC Gain2.) Mid-band gain3.) Frequency of pole4.) Frequency of zero

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 18, 2019, 11:53:49 pm
content: Quote from: TimNJ on April 18, 2019, 10:55:54 pmThanks for the reply. I forgot to mention that I dont have acess to custom wound switching transformers. I also have 0 idea how to calculate them, what core materials to use and everything. It is much easier to just get a part thats already available. I plan to power the controller with a capacitive divider, for now. Later I might go about creating a specific transformer for this purpose but I need bigger minds to help me do that. The transformer part is "Coilcraft HA4060".I simply have no patience of custom winding the thing. This way I get known numbers of the switching transformers like working frequency and peak currents and all the other stuff, that I would have had to measure in the first place. Maybe in the future I might end up teaming up with some switching transformer manufacturer, but that wont be any time soon since I really just want one or two pieces, no company in their right mind would support that.And I have no clue how am I going to solve the issue with the feedback. I dont know what values to choose and or how to do measurements on the original circuit so I can determine the values based on measurements..

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2019, 12:33:40 pm
content: Yeah, lifting ground won't work because you need a change in LED current to transmit a signal, and that current has to flow out the ground, so the voltage sensed by the error amp changes with load...What you can do, is make a little local supply, say 10V or so, with a zener shunt regulator, or an LR8 or something like that. This supplies the error amp, which should be TLV431 (note the voltage limit!) for lower current consumption. The "cathode" current can be cascoded into a pass transistor that drives the opto, or the whole thing supplied from the low voltage supply (either way, you need to handle the dissipation caused by the couple mA maximum consumption).BTW, the opto symbol is upside down?Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 19, 2019, 09:12:54 pm
content: Quote from: T3sl4co1l on April 19, 2019, 12:33:40 pmThank you Tim, in the ideal world I would have had a tap at the tranformer for the 431 and the opto which would have been propbably the best but overkill solution. If I would have had a custom tranformer that would have another secondary for the tube filaments (6,3V) then I would have used that. But I think this might be the best solution for my current setup. Simply just a shunt regulator.. now just to measure the current and choose the proper value for R6.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 19, 2019, 09:55:24 pm
content: Yeah, heater winding would do perfectly... ah well.That's why I added positions for an aux winding on this general-purpose power supply board:https://www.seventransistorlabs.com/Images/100WPowerSupplies.jpgthey've mostly gone unused, but are there for when it's needed.(I did make one, a 150-300V 100W model, which uses this aux secondary winding.)Also what's nice about custom transformers, and having a bunch of bobbins in stock.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 20, 2019, 03:35:18 pm
content: Quote from: T3sl4co1l on April 19, 2019, 09:55:24 pmThat looks hella professional. The big deal with the heater winding if there would be any, is that for an average amplifier like mine for example mine, two power tubes and two pream tubes, It requires at least 4A of output current with absolutely no headroom, 3A for the power tubes and 900mA for both preamp tubes. So id say a 30W winding would be ideal for an average amp (6,3V 5A). Maybe sometime in the future if I get a chance to work on the transformer with a professional SMPS transformer manufacturer. But the big deal is I got no idea how to calculate the transformers at all. I may ask Coilcraft if they would be willing to help out but I doubt any of that will happen.So I guess its only left to do measurements and go ahead build the thing. for the FB. I just hope it will be sub 5mA cause then I can simplify things and not waste incredible amounths of power lol.

author: TimNJ
author_rank: Super Contributor
timestamp: April 20, 2019, 03:52:01 pm
content: I think you are smart to not inflate the scope of your project by using an off-the-shelf transformer. My experience in designing SMPS transformers is fairly limited, but I can tell you a few things.1.) Getting a first “working” prototype is not that hard, even if you have little experience. But, optimizing the transformer can be quite a thought experiment, forcing you to think in terms of magnetic/electric fields, circulating currents and so on.2.) Hand winding a transformer is not hard at all! Getting your hands on all the supplies can be a bit challenging, but these days, you can buy sample kits on eBay inexpensively. For example, you might want various diameters of enameled wire, litz wire, triple insulated wire (TIW), TIW litz, poly tape (the yellow stuff), Teflon tube etc.It’s probably not worth the trouble at the moment. But sometime in the future, it may be worth it to give custom a shot.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 20, 2019, 07:19:49 pm
content: Quote from: TimNJ on April 20, 2019, 03:52:01 pmVery well said, to say my first ever HV experiment was a hand wound transformer and it was working better than expected but it definitely wasnt powerfull enought- 10W is not really useable for anything other than preamps and the ferrite was not glued and it was screming soo..but it worked. I much rather use the off the shelf stuff because the specifications are already there measured and I only work with those value instead of guesstimating and I really cant calculate that stuff, wire width inductances coupling coeficient and other stuff. So I did make a hand wound one but it was less than ideal. And also the enameled wires are not cheap. Their maybe look cheap for you but for some reason all the wires I would like to buy have either crazy postage and or crazy price.About the overinflation- its MUCH cheaper for me to buy a switching transformer that was designed more or less for the application im using it at. And a whole lot simpler. The first transformer I got I payed for and then now looking at the transformers I realised I can ask coilcraft for samples so I did and hopefully, the transformers will arrive so I can have test PCBs to experiment with.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 21, 2019, 12:53:02 am
content: XFMRSmay be more likely to prototype small quantities, or others that I've since forgotten; and also, any local motor rewind shop will likely have the tools and materials to do the same.Don't expect an amazing design from any of these sources, though -- to get that, you'll have to supply at least a basic drawing, preferably a drawing accurate down to the last turn, and designed based on transmission line transformer principles, and, probably, based on a lot of experience too.Custom voltages don't preclude the use of commercial parts, but it does severely limit the choice and performance. For multiple outputs, consider multiple single-output transformers wired in parallel (parallel primaries, of course). Any extra aux windings, of course, just leave open. (By the way, don't be tempted to use one as secondary-side aux: the pri-aux insulation is usually not full reinforced. If the datasheet says it is reinforced, though, that's fair game!)Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 21, 2019, 07:01:07 pm
content: Quote from: T3sl4co1l on April 21, 2019, 12:53:02 amYeah about the aux windings- no I only use the transofmers as specified in the datasheet. Now that im thinking about it, a all in one powersupply would be the ideal thing to do. 6,3V 35W for heaters, 400-600V for anodes about 80W, and another aux that would deliver almost no current , in some tube amps there is a -50V supply for biasing the output tubes. In cathode biased circuits you only need the heater and the HV, but cathode biased amps have their drawbacks, I would definitely want to try and make a fixed bias amp at some point. So yeah 6,3V 35W, -50V 5W, 400-600V anode voltage at about 80W of power would be ideal, a replacement compatible with most common amplifiers.I would like to do that but I have no idea how to calculate SMPS transformers at all and I cant really find literature that would explain it to me at the level of my understanding. But I will very likely do something like that as a grand finale for the PSU.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 27, 2019, 10:16:35 pm
content: Since I found that blowing with a fan on my original HV PSU was UNACCEPTABLE I went and redesigned the whole thing. This time using the TL494 as the controller. Operating frequiency will be set to 50kHz. Also have a soft start function, NO OPTO ISOLATION YET. Im still working on the mains powered solution.So basically I want to listen to my amplifier while I work on its powersupply some more without that fan blowing on the PCB lol. The reason the fan has to blow on the PCB is because i made the traces to thin (2mm) for the required power about 60W. It would require at least a 3,5mm trace with...but not to worry this time I bombproofed the thing and went 6mm trace width where I could and massive ground and power planes. And my pull is to tin it with liquid tin or the traditional handsoldering, depends how fast I can get it doneThe TL494 should give a way more stable output that I could ever get with my hacked together quad op amp controller I designed previously.The TL494 also extends the operating voltage up to 40V. About the efficiency- I have no idea what to expect so far, I will find out after loading and measuring the characteristics of the powersupply.(The board layout is not done completely.)EDIT: The IGBT will be mounted vertically to a heatsing not to the PCB (its also related to the not completeness of the board..)

author: Circlotron
author_rank: Super Contributor
timestamp: April 27, 2019, 11:31:38 pm
content: On your schematic the TL494 outputs are open emitter so you need to put a pull down resistor. Probably something like 470R, someone could suggest a value?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2019, 03:57:41 am
content: Gotta have a pull-down for that to work! The "emitter" outputs are just that, pull-ups only (or, well, pulling to the respective "collector" for the most part, but as shown, yeah).Flyback isn't very good for TL494, and especially not voltage mode. Why not another equally classic, easy-to-use controller like UC3842?Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 28, 2019, 11:09:43 am
content: Quote from: T3sl4co1l on April 28, 2019, 03:57:41 amI did actually make a SMPS based on the UC3842, but the output was rather noisy, very noisy electrically and audiably. I think it is due to my design but for the intended use it was not a big deal. With the TL494 I had so far only positives compared to everything else. I dont really like the 3842 or any 384x because I dont really see the function of a current mode controller. Its also non ideal for light loads. At least thats what I can tell from my findings.I SAID ITS NOT COMPLETEYeah I gotta look at it a couple more times before im sure that everythings as suposed.. Would 3k be enough for the pulldown?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 28, 2019, 05:09:21 pm
content: The fundamental reason for current mode, is because the inductor's state variable is current.Control the current, and you never have to worry about exploding the switch, overheating anything (maybe), or fusing the input or output, because current is limited, period.Then, you control that current, to regulate voltage. There's no LC filter (as in a voltage mode forward converter) to make your loop impossible to stabilize, compensation is straightforward. Instead, the L is in the current loop, and the current loop and C is in the voltage loop.The biggest drawback to voltage mode controls is exploding transistors due to unlimited transient response.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 28, 2019, 06:06:09 pm
content: Quote from: T3sl4co1l on April 28, 2019, 05:09:21 pm"The biggest drawback to voltage mode controls is exploding transistors due to unlimited transient response."That statment makes sense...actually its what im experiencing with my converter. I threw out the 3842 as a no go because I have used it in the past and wasnt really the best ever I seen. I have blown so far 5 fets on my pre pre pre prototype converter. It was getting as hot as the blazes of hell maybe even hotter (MrCarlson). Then that got fixed by puting it on a beefy heatsink and still died after a couple hours. The only transistor that survived all so far is the G30N60. IGBT. And that does heat up but but not so dramatically and id rather blame my PCB for that heating than anything.Im also not as familiar with the UC3842 as with the TL494 but I guess a look at the datasheet can change a lot of things withing a couple of minutes. The biggest problem I see with the UC3842 is current function. This may not be a problem with the mains powered PSU, but it sure is with the 12-24 range. There are simply too high currents for a standard resistor to sense the current. I supose I could calculate resistance to get 70W max out of the controller and get the resitance and create a resistor on the PCB by calculating the trace resistance to create a quite precise shunt. Just have to remmeber not to solder coat it. I dont have a lot of the same switching transformers so I can make only 3 more prototypes, one is the TL494 one other one could be the UC3842 and I can decide wheter to fit it with the GA3459 that has a slightly higher inductance and get 20A peak currents at 50kHz at 5V or the GA3460 that has a lower inductance and gets 50A of peak current at 50kHz at 12V.Yeah I will look into the UC3842 and try that one as well.One thing I cant understand at first glance is a lot of the schematics I see on the interwebz like the one I attached dont have direct feedback. Its totally feedbackless? I guess it knows the voltages by the sensing the transient? That would be my only guess. And the losses within the transformer are low enought to not disturb any other rails?Now seeing how it kind of works, I can see what the problem could have been with my original design. Tho I was 14 at the timne of designing that 10-24 input to input voltage-60V 50W converter. It has a lot of flaws xD , but interestingly I do remeber that the transistor was not heating as much as the diode did, so the fet did give a damn unlike the diode, that was burning hot without a heatsing and even with the heatsink it gets to a modest temp. Im getting off track.PS: I just noticed one thing in that schematic, the voltage is hard set I guess? How can I vary the voltage because the output should be settable anywhere between 240V up to 500V?

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 28, 2019, 08:24:43 pm
content: Alright, so I went trough some Flyback controller datasheets, new ones old ones, and I figured out how the feedback works on the schematic has no optocoupler. Very interesting indeed how it works using the aux winding to power the chip and sense the voltage at the output at the same time. But sadly that is not an option for me since I have a transformer that has no aux windings HOWEVER, I found a lot of great controllers like the LM5022. Requires a miniscule amounth of external parts, its a low side controller specifically for boost applications and it does SEPIC and Flyback controller. It has an extremely wide boltage operating range (6-60V!) and it really does all the things by itself. All I would need to do is to determine the CS resistor, frequency, the feedback and a really stable and simple SMPS is born..hopefully..We all know its never that simple.Looking at TIs library collection of flyback controllers, there isnt really a need to go with old classics other than if it costs a lot more than the classic, but really the features on these things should be better overall.So far these are the chips I have checked out:LM5155LM5022And those seem to be the best I can get for my specific needs. The schematics include easy Opto isolation options too or go non insulated, but the application I could see that in is when you power the converter from low voltage inputs like a PC powersupply which is known safe. But the big deal with PC powersupplies is that the output ground is mains ground reffernced, so if you connect a computer to it it automatically becomes a ground loop and there is no point of trying to supress that, its way easier to just isolate the input from the output so I might just go with either the LM5155 or 5022. First I have to make sure if its even available for a regular person like me. Great i searched for it because both these chips can do me good with the direct mains input and also the low voltage input converter.(Datasheets)LM5155http://www.ti.com/lit/ds/symlink/lm5155-q1.pdfLM5022http://www.ti.com/lit/ds/symlink/lm5022-q1.pdf

author: oPossum
author_rank: Super Contributor
timestamp: April 28, 2019, 09:48:14 pm
content: Quote from: SK_Caterpilar_SK on April 28, 2019, 06:06:09 pmThe winding used to power the UC3842 also provides feedback. The various output voltages are mostly a matter of turns ratio.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 28, 2019, 10:15:38 pm
content: Quote from: oPossum on April 28, 2019, 09:48:14 pmYeah I just said that in my last post before this one, thanks for pointinf out tho, if you could explain me how it works a little more in depth.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 29, 2019, 12:51:36 am
content: Quote from: SK_Caterpilar_SK on April 28, 2019, 06:06:09 pmYou were probably going the wrong direction, leading to positive feedback of frustration.Bigger transistors have more capacitance = more switching loss, both in the controller/driver and the transistor. IGBTs are also only effective at higher voltages. If this was another low-voltage application, that would be a problem!You can of course mis-design a current-mode switcher to explode. It's a much more straightforward design process to design one correctly, in comparison to a voltage-mode control that needs several hacks (soft start, current fault, lead-lag compensation with a zero in the filter) to behave acceptably.(Of those, you're already familiar with soft start; it is what it says. This ramps up PWM slowly, which works when the output is not shorted and when the input is applied suddenly (the usual case). This fails if the output is overloaded or shorted, and this also fails if the input drops momentarily, or a transient load is applied. For that case, a current fault can detect high peak currents (usually with a current transformer and comparator), and retard or stop switching, and maybe restart from a soft-start condition. PITA if your load was expecting stable voltage under transient load, but whatever. The compensation is jargon for an output filter that has ESR as a critical part of its behavior (typically somewhat lossy electrolytic capacitors are used, for their useful ESR), and the error amp has an R+C across both feedback resistors, to give a slight edge in phase margin near cutoff. Effectively, we try to speed up the error amp's response just a little, but also shelf its response just right, to avoid oscillation. Well, until the electrolytics dry up at least...)QuoteIf you need further convincing (and don't have any on hand), build the block diagram yourself, with a comparator (LM393 will do), logic (discrete transistors or a CD4001 or 4011 will do) and driver (complementary emitter follower 2N4401/3 will do). Uh, and oscillator of course. 555 in a pinch, but a... well, anything that can make spikes will do, so among RC oscillators you probably want to use a diode across the timing resistor to get one short edge; 555, CD4093, CD4049, CD40106, etc. will do. So, overall, 4093 probably the best since you can use two for osc, two for RS f-f. Or a spare comparator, that's fine too.QuoteWell not so much current as voltage. Newer controllers will happily sense more like 100mV there (LM5001 comes to mind, although that's a regulator (integrated switch), and I forget what's similar that's a controller (external switch), but that LM5022 is not a bad example). Which makes 10, 20A, or more, practical.So, two things:1. You can bias the current-sense node up with a voltage divider from VREF to ISENSE to shunt resistor. This raises the DC voltage at ISENSE, while lowering the AC gain slightly. Instead of a 0-1000mV range, you might have say 700-1000mV range (basically you lop off the bottom 700mV of useful ISENSE range), while only needing, I don't know, 350mV or so of shunt voltage.1a. You can combine this with slope compensation, which adds DC anyway, but also some AC (namely, from the RtCt pin), which compensates the current loop for operation in CCM (continuous conduction mode -- inductor current doesn't return to zero every cycle). So it reduces the active range on the ISENSE pin (also reducing the shunt voltage drop), and has the benefit of higher inductance (lower core losses).A note on peak current mode control: you need to operate in DCM (not CCM), otherwise chaotic behavior results*. Slope compensation allows a less-than-100% ripple fraction (i.e., Ip-p / 2 < Idc), although not too much less (50-80% ripple fraction at rated output is typical).*The underlying reason for this is quite cool: it turns out, a peak current mode controller is an electronic implementation of the Logistic Map, an iterated chaotic function. This function takes a parameter, which as the parameter increases, at first the behavior is nonlinear but reasonable, but suddenly it splits into a multitude of values that cycle between themselves from iteration to iteration (period doubling, limit cycles). The corresponding circuit parameter is, guess what -- inverse ripple fraction. So, keeping the ripple fraction high, prevents chaos. Chaos is undesirable in circuit, mostly because it causes increased ripple and a hissing sound.2. We don't need to use a resistor. Anything that senses the same current will do. A current transformer is a typical choice:https://www.seventransistorlabs.com/Images/Mag_Amp_PSU.png(incidentally, speaking of slope compensation -- with the values and components shown, this circuit needs slope compensation! It's an old circuit.)Note that transformers won't sense DC. We can sense partial DC, as long as it returns to zero every cycle ("pulsed DC"). Which we can ensure here, by using a diode on both sides of the transformer -- well, not explicitly so on the primary, but we can ensure that current is only drawn in pulses, when the transistor is switching, so it works out the same way. A large resistor (1k here) across the CT winding dampens the "reset" pulse, reducing stress on the output diode (FR102).That looks like this,https://www.seventransistorlabs.com/Images/Snubber_103Z.jpg(Actually a different module, with a lower ratio CT; same idea, in any case.)Both of these also show a key improvement, a dV/dt slope snubber. Your attached also shows this (C8, D4, R11). This allows the transistor to turn off, say in 40ns, while the drain voltage rises, say over 80ns (depends on current, because the peak inductor current is charging the capacitor at dV/dt = Ipk / C), greatly reducing turn-off losses. (Turn-on losses aren't usually a big deal, because there's not a lot of inductor current to pull down on at that time.)The RC value can also be chosen to dampen the free ringdown (when the inductor's current is discharged, before the next cycle begins), saving some more EMI. (The reduced dV/dt already saves some EMI.)QuoteDepends on what's required. Normally, a TL431 and opto is used for feedback. The 3842 is wired as an inverting amp (no compensation), so the opto commands whatever peak current from the 3842 it desires. The internal comparator handles peak current, so that's perfectly fine. The 431 then regulates voltage by controlling that current.This works fine for one or two outputs, but the problem with multiple outputs is cross-regulation.Regulating from the aux winding is the same thing: the aux output will be damn accurate, but the rest will be soft and vary up and down with load.Cross-regulation is driven by leakage inductance between secondaries. Ideally, you want them all very tightly coupled, so they all receive the same flyback voltage, no matter the current draw on each. Practically, 10 or 20% cross-regulation is reasonable. Better is achievable with a carefully designed transformer. Worse is expected from a naively designed transformer...If you need better cross-regulation, and the outputs are common-ground (as your heater and B+ outputs might be), you can use joint regulation. One TL431 controls the throttle, and its feedback resistor divider is fed by both rails. The regulation is the weighted average (weighted by the ratio of voltages and resistances) of the two outputs.For a tube amp, this means B+ doesn't fucking explode while the heaters are cold, or conversely, that the heaters just never even begin to heat up while the B+ is completely unloaded. Instead, B+ overshoots some, but not by an insane amount, while the heaters warm up a bit slower than normal, but eventually everything gets there.Like, I had to do that on this one,https://www.seventransistorlabs.com/Images/Discrete_Tube_Supply.pnginstead of a single 680k from +100V to TL431, it's actually more like 1Meg, and there's a, I don't know, 47k or something, from 6.2V to TL431. Same 18k from TL431 to GND.I built two of these; one is in an all-tube set,https://www.seventransistorlabs.com/Radio_20m/and one is in my Theremin (which is solid state, with the +100V for varactor bias and optional tube-based timbre circuitry). The latter may be regulated on 6.2V only, I don't remember (which is the main load, so that would be fine).QuoteYeah, like I said -- there are fewer things you need to get right in a peak-current-mode controller, and they are easier to get right, but you still have to get them right in the first place.You probably just didn't know at the time.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: April 29, 2019, 09:06:18 pm
content: Quote from: T3sl4co1l on April 29, 2019, 12:51:36 amSome of the things you mentioned in your post I am familiar with. The soft start is easy to implement but in practice, yeah youre right if input is suddenly lost and then reapplied and the output is loaded, the entire slow start is just like if it wasnt there at all.No thanks I dont really want to build the entire thing xD. It would sure uncover things but I can see how its working on paper, its just been a while since I looked in the UC3842 datashet as I said I was 14 at the time and I kind of developed a stigma arround it. Allaround current mode does not look so bad now to me. But the LM5022 seems awfully similar to the UC3842 in the datasheets.I would like to go with the LM5022, looks simple and seems functionally great too. I only have to do some datasheet searching and get the values done. Also the way I see it, I could technically swap the inductor for a switching transformer. I dont really know how to get the LM5022 into DCM. Also having read an article about DCM VS CCM, just to let you know 500V 200mA is not low power so CCM is unavoidable if I understood the thing correctly. (Inductor in the schematic in the datasheet of the LM5022)Are you telling me that I can change the sensitivity of the the current sense by injecting DC to the Isense pin of UC3842?Transformers sense AC thats pretty clear to me. I also do know how current sensing transformers work. So you basically worked arround not having an AUX winding and hacking one together with a current sensing transformer? Should work as far as I can imagine.About the Feedbacks you mentioned :For regulating two outputs you just average the signals? Thats kind of how I got that.In your case the most load will be from the 6,2V output, but in my case for now I have only one single output and that is for the HV. My powersupply can already as is do 65W output power at 450V, and im looking for a way to improve it to get the most power out of it with the least noise. Regulation can be tight because were only regulating one rail and yeah I dont know what else to say.The ideal powersupply I would like to design at some point has 3 outputs. 6,3V DC heater voltage which would get me at least 6A of current (about 40W), 50V DC biasing voltage (low power, really a couple of miliamps will do I would say 5W would be enought any day), and the hopefully adjustable 300V-550V HV output that would be at least 70W capable. Ofcourse this is assuming youre powering a single powe amplifier, if id like to go stereo which would almost be like a life goal to do for me (), would have to basically double the power of all. Maybe even go as far as 170W for HV if it would be used for one big fat mono amplifier.The power rating I guess all comes down to the switching transformer and the fet. I have no idea what tipe of a switching transformer I would use for a 115W total output power powersupply let alone the big fat stereo brother that would do double that. At that point I would probably consider just splitting the powersupply into the 6,3V heater supply combined with the 50V bias and the HV supply to be discrete alltogether.But im really getting ahead of myself. Previously the big goal was to make any HV powersupply that would be useable. Now the most recent was to create one that can give me quite the power and I also suceeded. So now I just want to make it more stable useable and create the mains powered version aswell. And then the next thing to do is to look into designing a switching transformer, hopefully get a hold of the knowledge and design a transformer that would perform as the ideal psu I want to present as a complete thing. 6.3V 40W, 300-550V HV at 70/80W, 50V bias voltage really low power 5W would be enough. And I dont know if such a PSU would be adjustable in that much of a range (200V range for HV that would not disturb the other rails so dramatically seems unrealistic) and even if not, making powersupplies for specific voltages would not bother me at all.But im REAAAAALLY getting ahead of myself.Now Im going to manufacture the converter with the TL494 to see the outcome, Im already looking into the LM5022 because I want to use that controller in my next design that should be more stable and less noisy.. hopefully more efficient too. Then the multiple output rail powersupply and then I might just feel complete enought to also make a speaker cabinet which is on my plans to do xD . All of this next to me repairing stuff, but without repairs I would not have the finances to even begin with a project like this. But im afraid its going to take me too long to get this one done.(why do I sound so dumb to myself when I read this back lol)PS: Thanks Tim for your massive help tho. Really appreciate it. And sorry for my grammar as you could have guessed im not native english speaking.EDIT: BTW would love to build that radio at some point but instead of subminiature tubes either with 7PIN miniatures or 9pins..makes em easy to source if they die. I probably have OCD because I was tripping hard when I saw the wiring xD . No offense but PCBs just look a lot more clean lol. I would love to built it at some point so I may aswel design a PCB for it..IF I will ever get to that day.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 30, 2019, 12:26:58 am
content: DCM vs. CCM, or more broadly the ripple fraction, is determined by the ratio of inductor voltage to inductance and frequency. So, to move towards DCM, use smaller inductor, lower frequency or higher voltage.Tim

author: Circlotron
author_rank: Super Contributor
timestamp: April 30, 2019, 01:00:09 am
content: Quote from: T3sl4co1l on April 29, 2019, 12:51:36 amCCM with a flyback converter is somewhat tricky. Say you decide to reduce the output so you reduce the mosfet on-time pulse width and this has the effect of *increasing* the converter output pulse width for a number of cycles until the transformer flux ratchets down to a level that matches the desired output. Much harder to stabilise than DCM.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: May 02, 2019, 10:54:21 am
content: Quote from: T3sl4co1l on April 30, 2019, 12:26:58 amThe LM5022 seems to be capable to do both CCM and DCM. It seems to work as DCM up until a certain load. Using the Coilcraft GA3459, which has low inductance or even the GA3460 which has even lower inductance, it might just stay in DCM mode. (GA3459 5uH, GA3460 2,5uH inductance). Also the primary resistance is very low, so this all may just be enought for the controller to stay in DCM.OR I could use a controller you would recommend. Because I simply cant know every single bit of info existing out there. So yeah I would look into other directions no problem just show me which way. Mos common controllers I know is the 384X the TL494,TL497 and these that I just found (LM5022 and others I mentioned in my post somewehre above).Im also looking at coilcrafts custom transformer request document, maybe try it out, see what the outcome will be.https://www.coilcraft.com/custom_trans.cfm

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: May 12, 2019, 09:14:06 pm
content: So Im back at this again and now that I see how the powersupply preforms, I want to take it up another level.Here is what I want to achieve:Input:90VAC-265VACOutput:6,3VDC 40W (3% load stability, necessary for tube heater life.)-60VDC biasing output (not much power required so ill just say max 3W, its critical to be stable as much as possible!)if possible- adjustable output 350V-500VDC 80-100W ( Regulated stable.)So far I dont know how am I going to achieve this. Im even thinking about using two powersupplies. One for the HV which now could be adjustable, and one for the heaaters 6,3V and the biasing -60V.Furthermore I dont know what topology to use. Flyback as far I know is only good up until 100W and to add on top of that, I know nothing about switching transformer design so I will have to check out a lot of literature. If someone could point me to some really usefull literature about designing a switchmode transformer and what topology to utilize I would be thankfull.I have high hopes for you Timhope you have something to send me a link to.Btw I have been looking at your radio project and damn I like it, I want to build it but with 9pin tubes, I think it will be better in the long run. The only drawback is that its not FM so in my location if you listen to the same radio station over at AM and FM only the news are the same and everything other over the AM band is for old people and the FM band is the mainstream. For that purpose I want to build a pulse counting FM tube radio. I think you already saw it somewhere. Found the thing over herehttp://diytuberadio.blogspot.com/2011/02/love-grandfather-tube-radios-diy.htmlThanksAdam.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 13, 2019, 01:24:39 pm
content: Flyback for both is fine. Or forward for heaters, but not for HV because flyback is better there.I have an FM radio project too that I haven't documented yet: it uses a 6688 RF preamp (double tuned grid and plate circuits, BW = 20MHz), 6J6 single balanced mixer, 6C4 LO. Some of the goals were developing a feel for grid impedances, which are significantly lower than the cold capacitance, when heated and biased. In particular, the 6688 is around 500Ω || 18pF at 100MHz, I think it was. 6J6 is higher impedance (grid to grid), and its cathode input impedance (which is where the LO is introduced) is basically cathode resistance (i.e., ~1/Gm, and that's total Gm of both halves, since they act in parallel for a cathode-LO-input SBM). That constitutes the front end, with an IF output at 33MHz into 50Ω and a final BW of a few MHz.The IF strip is three 5702s, double tuned for about 200kHz bandwidth and a shitton of gain; except for the first stage which is single tuned (matching 50Ω to the grid), but combined with the front end's IF output network, it's actually triple tuned.The grid impedances are around 10kΩ plus some pF at 33MHz. Combined with about 5mS transconductance, that's about 50 gain each, but it's more like 100 because the plate load impedance can be matched higher (closer to 20kΩ I think).Keeping them from oscillating was a bit tricky. The Cg1a for 5702 is relatively high, for high gain at 33MHz. I'm pushing the maximum stable gain, a figure which has to do with the gain and phase shift of the input and output networks, and the feedback between them. There is some neutralization, where the grid network is returned to ground through 100pF, and a small fraction of the plate signal is cap-coupled to that node. The plates also needed shielding, for which I just rolled up some tinned steel, since good luck finding originals? (The 5702s are again mounted in fuse clips, which hold the shield which hold the tube.)The last 5702 is biased harder, and loaded with about 5kΩ (single tuned) for maximum power output. This is tapped down for a ~1kΩ output impedance to drive the detector. (The reason being, the higher plate impedance maximizes gain and output power, while the lower output impedance gives more drive for the detector.) This drives a 6AL5 detector (half wave doubler configuration, so its average impedance is fairly low), which generates negative detected AM (where applicable). This also serves as ALC, as the grid bypass caps (the 100pF's) are chained together with ~10kΩ ferrite beads and biased with this voltage. For FM, this gives some limiting action already, and for AM, this gives a somewhat logarithmic response, which is fine for detection purposes.The final IF is further coupled to a 6BN6 sheet-beam discriminator. These are only practical at quite low frequencies (~4MHz IF), due to how the mutual impedances work out, and the width of BCB FM. But IF is 33MHz? For this reason, I have a 2nd LO at 29MHz (a 5744 submini triode), and a diplexing filter network (two different L||C traps, coupling IF to 6BN6 grid, and LO2 to 6BN6 grid, but isolating LO2 from IF final, and vice versa). This gives about 10V of both at the 6BN6 grid, which due to its sharp transfer function, acts as a mixer itself, generating the 4.5MHz IF3 internally as it were.The 6BN6 is a neat tube, but limited on options, given commercial FM modulation depth, and the beam conductance.A word about that: the electron beam itself is made of matter, with mass -- electrons. To physically move it around, requires work. That work manifests as a resistance component. The work increases as frequency increases, so the resistance decreases. (In fact, apparently it goes as 1/f^2.) There is also a factor for the beam's space charge working against the driving electrode, which is conservative so manifests as capacitance. It happens that the capacitance is dominant, and for most "high performance" tubes (the best ones of the 40s and 50s, and most from the 60s), the dynamic grid capacitance (at nominal bias) is about 80% of the cold capacitance. The capacitance varies with bias (because of how much beam is passing the grid), and with emission (because the space charge between grid and cathode acts as a spring).The resistance is much higher than that reactance, so you can still get reasonable tuned Q, and the tube's GBW is still more or less constant with respect to center frequency.Another aside -- the band width of a tuned amplifier is limited by the source or load resistance, and the minimum reactance of the circuit. It seems all known devices (BJTs, FETs, tubes) have a transconductance-with-capacitors characteristic, with some loss element for the input and output, and none have a fundamental voltage-source-with-inductors characteristic. So, while the same physics applies for both, it seems we only need be concerned by the case with capacitance as the limiting reactance.Then: the impedance of a tuned network is Zo = 1 / (2*pi*Fc*C), and if C has some fixed minimum, then at a given center frequency Fc, the characteristic impedance Zo has a fixed maximum. Where we have some source resistance Rs or load impedance RL, we have a Q of R / Zo, and a bandwidth BW = Fc / Q. (When Q < 1, it may be more meaningful to think of it as a combined low-pass and high-pass network, and you can consider replacing the inductors with resistors, or with proceeding stage outputs, i.e., making a DC-coupled amp with no LF cutoff (no highpass). In that case, BW is the baseband bandwidth, i.e., the HF cutoff.)If we have more grid C, we need lower L for the same Fc, and get higher q and lower BW. If we reduce R, we get higher BW, but proportionally lower gain.So, at a given Fc, an amplifier exhibits constant GBW. Since grid conductance varies with frequency, we should expect GBW to change with Fc, but in practice it's not a big factor.So, back to the 6BN6 discriminator.An already-modulated electron beam carries momentum along its path. This manifests as a transconductance between grids. In a tetrode, there is a G_g1g2 which is nonzero -- but the inverse is not typically true, i.e., G_g2g1 is extremely small. This is called a nonreciprocal effect, and happens because the beam acts like a conveyor belt. (Nonreciprocity is very difficult to realize without spending power -- of course, we're talking about an amplifier tube here, so we're doing quite a lot of work, biasing this tube, and this is physically consistent.)This is used in the 6BN6 to excite the second grid. An impedance is connected to g2, the mutual conductance develops a voltage in it, and that voltage modulates the plate current. When that impedance is a tuned circuit, the phase shift is frequency dependent, and we get a plate current that looks pulse-width modulated with respect to input frequency. This is filtered down to "DC", and hence FM is detected. Slick as hell, isn't it?The downside is, that mutual conductance can only be controlled by cathode current, and only over a modest range. The Q factor of the network needs to be quite low, so that its bandwidth is comparable to the modulation depth -- 200kHz width at 4.5MHz Fc is pretty low, meanwhile the impedance needs to be very high, because the transconductance is very low (in the uS). I ended up using a lot of turns of fine wire (I forget how many, maybe 50-100 of 37AWG on a 9mm form), with a ferrite slug to tune it, to get that little extra impedance out of the network.The distortion still isn't terribly great. The limiting is quite good -- no fading is apparent, and the response is just as you expect from a modern receiver, as you tune across stations.The overall structure -- you might notice that there's a lot more tubes in here than a commercial FM receiver, of course partly just because I don't want to have to optimize it that much; but also because I want some more options with this receiver. In the front end, all the tuned networks are pluggable, so they can be switched out for, say, 120MHz (aviation) or 144MHz (amateur 2m) bands. The IF strip is a separate module connected by BNC jacks; if I want a lower or narrower IF (say for AM voice or FM NB), I can construct one. Or add a 50Ω output to the 33MHz final IF, and connect that to a 2nd IF strip, to the same end.Pictures!Power supplies -- back on topic in this thread, I use a pair of single-output flyback supplies. They don't seem to generate much noise in the relevant bands, so reception is fine. (They are cleaned up a bit, but I doubt they would pass FCC Part 15, particularly the HV supply which has some nastiness coming from the transformer -- bad windup.)https://www.seventransistorlabs.com/Images/100WPowerSupplies.jpgMiddle and right, 150-300V 0.5A (set for 150V), and 6.3V 10A.https://www.seventransistorlabs.com/Images/FMRadio2.jpgFront end, top view (shields off)https://www.seventransistorlabs.com/Images/FMRadio3.jpgBottomhttps://www.seventransistorlabs.com/Images/FMRadio4.jpgPluggable networks (FM BCB)https://www.seventransistorlabs.com/Images/Radio_IF_Filter.pngAnalysis of 6J6 plate network (front end IF output; left network in above pic). R9 is Ra-a (plate resistance), inductors are air core and coupled as listed, and capacitances of plate (Cga + strays) and trimmers shown separately. Note output is series tuned into 50 ohms -- flexibility in topology is key for good optimization.Cheers!Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: May 13, 2019, 08:22:03 pm
content: Quote from: T3sl4co1l on May 13, 2019, 01:24:39 pmMan thats one hell of a big fat reply xD. Absolutely amazing Tim. And I love the radio stuff maybe end up some day building that pulse counting tube radio I showed because of its relative simplicity and yeah lol.Here is the thing. I dont know how to design smps transformers properly. I see your powersupplies are quite powerfull and you probably did the math on your transformers yourself. So the deal is, I want to do my own math too lol.At this point I decided to have two separate switching supplies. One for the heaters and negative bias voltage, and the other one will be the big fat 100W 500V smps. This way I can really get tube lifetime out. One of the most important things with vacuum tubes is to keep the heater voltage at an exact level with the least heater voltage deviation. As low as possible. Like hopefully within 1-2% is achieveable at all. And this way the HV can be also regulated tightly which works out just about perfect this way.And btw you kind of forgot about my problem of not having the literature for the job so if you could please point me to any literature. Or help me designign my transformer, I would be more than thankfull.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 14, 2019, 02:31:10 am
content: I'm a terrible reference for literature unfortunately; most of what I know has been synthesized from piecemeal articles, and experiments, supported by a strong foundation of theory. Hopefully others can volunteer something...Offhand, these may be useful:Magnetics Design Handbook, Unitrode/TIhttps://www.ti.com/seclit/ml/slup132/slup132.pdfTransmission line transformers --http://een.iust.ac.ir/profs/Tayarani/files/transmission%20line%20transformer.pdfHandbook, Amidonhttp://www.introni.it/pdf/Amidon%20-%20Transmission%20Line%20Transformers%20Handbook.pdfAn original, in a sense; G. Guanella, New Method of Impedance Matching in Radio-Frequency Circuitshttps://hamwaves.com/chokes/doc/guanella.1944.pdfI emphasize transmission lines, because they are the most general, and in my opinion not onerous to understand (but, prove me wrong; these things come naturally to me so I underestimate how much complexity goes into them).The basics are this: a transmission line is formed by two pieces of wire being nearby.That gives a characteristic impedance (which depends on the relative cross section only), and a characteristic length. We instantly know all the other high-frequency properties of the structure (delay, cutoff frequency, leakage inductance, parasitic capacitance), and need only ask the impedance of the core to figure out the low frequency properties (magnetizing inductance, coupling factor).In a transformer, we have a primary and secondary wound together, for example as a pair of single layer (solenoid) windings. If these are wound in the same direction (say, clockwise, left to right, start to finish), then they act like bifilar wire wound edgewise, and the impedance is that of the bifilar pair (well... nearly). The length is simply the wire length.Or we can just wind bifilar wire flat as usual, and then we have two helical windings within each other, 180 degrees apart. The impedance is again the bifilar pair (...nearly).Or we could wind two layers, one left-to-right and the next right-to-left. Now the helices are opposite handed, and the wires don't perfectly line up -- they're crossing over and under each other, every turn. Well, in this case, we still have a given wire in proximity to others, it's just less uniform. (As long as we aren't considering waveforms with edges as fast as the electrical length of a single turn, we don't care.)What violates this sort of approach, is having multilayer windings. Say we put down two layers of primary, then two layers of secondary. The first primary layer "sees" its neighbor, not the secondary, so it doesn't couple directly to the secondary. And likewise for the far secondary layer. The inner layers see primary and secondary respectively, but also see the outer layers. We see two things in this situation: the image currents from the outer layers flow on the inner layers, dramatically increasing their losses (proximity effect); and, the impedance between outer layers is a good, what, triple or so the impedance you might've been expecting given the layer-to-layer distance. But the wire length is double, so the inductance is sextuple and the self-capacitance (capacitance between ends of a given winding) is equal to the isolation capacitance (between windings).In short, multilayer windings have considerably lower bandwidth, and fairly higher impedance, than a proper single-layer winding in transmission line style.What if you want a high impedance transformer? Well, you can open up the distance between wires (higher winding pitch, thicker inter-layer insulation); but this does waste a lot of space. You can at least use a longer bobbin (to get a wider single layer winding), or maybe a toroid if you don't mind winding one. You also tend to need a lot of turns, though, especially at very high voltages. So the reduction in bandwidth is inevitable, and at some point you'll need to use another approach, like a resonant supply instead of a switcher.What if you want a low impedance transformer? Use wider wires -- multifilar, lots of wires in parallel abreast -- or foil. Planar transformers are very attractive here, where you can stack alternating layers in parallel (primary and secondary), more than halving the impedance compared to a single layer pair.You can use some cheats, like connecting windings in series at DC, but stacking them (one diode per layer) so they act in parallel at AC (the capacitance between windings cancels out). CRT flyback transformers are made this way.I did a sort of this in this module,https://www.seventransistorlabs.com/Images/DCDC_800V.jpgwhich is a 12V input, 800V output (adjustable 100-800) module, and uh, 50W or so rated, I forget exactly. The transformer has the windup,https://www.seventransistorlabs.com/Images/DCDC_800V_FoilWindup.jpgthe primary is low impedance (12V DC input, some amps), so foil is appropriate. The secondary is high impedance (400V and fractional amps). The two sections are wired in series, and the rectifier is wired as a bipolar output (+/- 400V). The "-400V" node is merely grounded, giving 800V total output.Here, it's not so much that the secondary layers act together -- they can't, there's a foil turn between them -- but that they are in the same environment, it's symmetrical, so whatever happens to one, happens inversely on the other. With the diodes similarly symmetrical, the output voltage is symmetrical, and the common mode noise is symmetrical (well, around the middle of the primary it is).This is the key feature that my 100W offline supply was missing -- I didn't consider the relative voltages at the start and end of the windings, and ended up getting one backwards, so the full switching waveform gets induced across the isolation capacitance. Huge fuckin' common mode noise. This module, well, it doesn't actually matter any because it's common ground, but -- if it were isolated, it would be a far sight better, despite its much higher output voltage.The windings are also pretty short, like 1-2m of wire, so the bandwidth remains high despite the impedance mismatch (the impedance of a round wire winding sandwiched between two plates, and a couple layers of tape, is around 50 ohms, whereas a kohm or so would be more appropriate). In fact I see very little if any overshoot and ringing on the waveforms, I was quite impressed. (Part of the short windings is the oversized core: it's good for about 100W in flyback, but only being used for 30, maybe 50W.)Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 08, 2019, 09:49:35 pm
content: So it has been a while since I posted something and now its time for a question.I have not had any time to make the powersupply at all. I still have the second version on paper not an actual working device but I have got some time toi sniff arround my prototype. the previous problem was that the entire PSU seems quite inefficient. The mosfet gets blistering hot and so does then switching transformer.I have looked at the gate voltage and it seems fine to me, but the transformer has an extreme amounth of oscillation. More specifically I was measuring ground to drain of the mosfet. That said on the high side of the G voltage it pulls short 2 ground on the drain (just saying so you dont have to figure out on your own.). Could this be causing the heating of the transformer and the mosfet? Interesting is that any capacitor in the input (bypass capacitor- electrolitic) right close to the switching transformer it gets very, very hot.I dont really know why this is happening, so far my knowledge about SMPS are rather basic. I did design another powersuply completely, but since I did not know about this issue Im pretty sure it will happend again.I have hope in your reply Tim. Would just a snubber network solve this or it is something that needs a more proper solution. I have a feeling it is going to require a proper solution.On the oscilloscope where there is only one waveform I have measured between D and S (G30N60-its not a mosfet-IGBT but a really expensive one that works really well, does not heat up as much as a IRFZ44. This heating issue stays a problem even for really low on resistance mosfets like for 100A above mosfets). The frequency of oscillation is 840kHz.So how can I make it more relyable and efficient? Assuming the controller will be a TL494 in the future powersupply. Also I would not mind using a different chip if that makes it better.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: June 08, 2019, 09:53:02 pm
content: Also in reply to my previous reply, the first waveform where the oscialltion is way more pronounced im switching the transformer at 75kHz (unintentionally, I have set it to 50kHz just as specified by the manufacturer but seems under load it changed the whole thing, it is the fault of my crappy controller, the traces all act like antennas.The second measurement was taken at 30khz switching frequency.Also in the second measurement the 1st probe is in 10x , I forgot to set the scale properly on the scope.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: June 09, 2019, 02:20:21 am
content: Looks like a shitton of leakage in the transformer.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 11, 2019, 07:36:54 pm
content: Okay...back at it but quite a bit dissapointed and hopeless this time. The latest circuit with the TL494 is not working the way I inteded it.. The controller spazzes out when the tubes begin pulling a whole lot of power.. It can cope with resistive loads great but cant handle dynamic loads. It simply wants to regulate the voltage too tight that it just goes nuts when the tubes want to pull more power (bass note or something). It spazzes out goes 90% duty and trips the OCP on the 13A 12V powersupply...optionally it burns a mosfet.So its not working. I had 3 tries at this problem. LT3751 which did not work at all. Not even a single pulse from it. Custom controller which burned five mosfets before it worked at all, and the TL494, which keeps spazzing out tripping OCP and burning mosfets. My frustration has reached beyond borders. I have no idea what to do at this point.I think this project was doomed the day I made the decision to go on. I spent too much money and time on the project that did not work so im kind of hopeless at this point.For the ones supporting me and helping me thank you all, but this project inevitably met its end with a big failure sticker on its archive. Unless someone knows a proper SMPS design, because apparently I dont at all.

author: FreddieChopin
author_rank: Regular Contributor
timestamp: September 11, 2019, 08:14:58 pm
content: Quote from: SK_Caterpilar_SK on June 08, 2019, 09:49:35 pmDumb question but is your probe compensated? Connect it to square wave test pins on scope and adjust until it's perfect rectangle.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 11, 2019, 10:40:41 pm
content: Checked against control and other square waves on the poversupply board.(fet drive signal from TC4420). The transformácie by that time was already through hell and back but i think I saw such ugly waveform because I was running a IGBT instead of a FET. That original power supply is dead by now. (Funny it wasn't the fet nor the circuit itself that died but the voltage regulation that was horribly underdone.)

author: Audioguru again
author_rank: Regular Contributor
timestamp: September 12, 2019, 03:42:45 am
content: I was 19 years old in 1964 when I sold my vacuum tubes amplifier assembled kit (that needed its tubes replaced often) to an old geezer and replace it with a solid state amplifier that still works well today. I have not seen a working vacuum tube since then, but there is a store that sells a solid state amplifier with a couple of vacuum tubes glowing on top (not in the amplifier circuit) that are sold to old audiophools.

author: mrjoda
author_rank: Regular Contributor
timestamp: September 12, 2019, 06:03:11 am
content: Hi SK_Caterpilar_SK,I found this topic quite interesting. The idea of SMPS for tube (headamp) is in my head a few weeks (actually more than weeks). I started slowly, bought some books, read a lot of literature. The whole schematic is in my head... briefly...My ideas went down, when i found that isolated RF wire for primary winding is almost impossible to buy without selling a kidney. And insulation at least 4kV primary/secondary is another chapter. Chinese supplier for whole transformer is the cheapest and most available solution...The optocoupler feedback is quite issue. A BIG issue. Fortunately, i have access to bode100 in our company so it can by done.Maybe this topic is starter for me for comeback from ideas to project.And last point :your pcb from previous page is wrong and messy. EMC hell

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 12, 2019, 09:20:27 am
content: It definitely is a EMC hell, so far aiming for anything functionall.I do have a solution for opto isolating the output with clasic method (TL431 and PC817). I can send you the schematic for that. It loads the supply at 500V with about 2W. It gives a little load for stability. I simply shunt regulated the opto diodes voltage so I dont kill the TL431. The primary side of the thing is simply text book grade stuff, sufficient enough.Switching transformers provided by coilcraft are decent enough. I use the GA3459 for 12-24V to 500V conversion. Also the GA3460 does the same but the winding DCR is much lower and other things..I planned using the HA4060 to try with line voltage but currently I just have the transformer and dont plan on doing such a dangerous project.So far Im searching a suitable controller for the job. Not having bias windings in transformers is a pain, but solvable. If it would work out with temporary solutions I would go ahead and quote coilcraft for custom transformers but so far there is no point in doing that. Unless I find a viable solution for the first problem.

author: mrjoda
author_rank: Regular Contributor
timestamp: September 12, 2019, 09:55:40 am
content: A feedback of smps is never so easy as it looks. You have to think in frequency domain, not in time.check this article :https://www.onsemi.com/pub/Collateral/TND381-D.PDFit gives you a long no sleep nights and headache.TL431 is the most straightforward solution, but not the best.I based my ideas on Viper 53 from ST. I was not able to find any reasons why is not suitable for this task, but maybe someone with better experiences could find one.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 12, 2019, 11:46:37 am
content: The 431 is the simplest all around solution and I like the Viper 53 unfortunately for me still trying to make a 12-24V input power supply and the switching transformers I have don't have aux windings. And in general I find PSR way more confusing than voltage feedback from the secondary side.I would like to consider that option tho, I just don't have the literature to clarify some things

author: scatterandfocus
author_rank: Regular Contributor
timestamp: September 15, 2019, 12:50:17 am
content: I saw this thread some days ago, but I don't login to any sites from work machines and network, so I didn't reply.It's an interesting project. At least one manufacturer did produce some tube amps using switching supplies - Crate V series amps. They didn't go over well in the long run because of audio quality (noise) and generally poor construction. Keep in mind that these amps were not aimed at the vintage amp crowd. They were low priced tube amps, where the crowd isn't so picky as long as things work as they should and sound ok. I haven't seen any other tube amps that use a switching supply, but I haven't gone looking either. If done well enough that I couldn't hear a difference between it and a linear supply AND the thing is well constructed AND it doesn't introduce noise into other devices, I would prefer the more efficient supply.Oh,and I forgot about some of the scary failures of those Crate V series amps. Just went on a little reading spree about those amps, as I haven't heard anything about them in a long time now. Apparently Crate went out of business a couple of years after the release of the V series amps.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 15, 2019, 03:56:43 am
content: Dave Berning created a series of tube amps with DC transformers -- MOSFET choppers plus transformer coupling. IIRC, they ran around 200kHz, and the primary side used as many windings in series to supply the voltage required for the tube, allowing otherwise fairly difficult-to-use types like transmitter tubes (e.g. 1kV 100mA, a high load impedance) to be used down to DC.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 16, 2019, 06:49:57 pm
content: Hey Tim, or anyone really who knows the answer to this.How do I figure out what kind of capacitance I need on the input side of my powersupply (mains side).Assuming ill be operating in DCM at 100kHz with peak current of 2.5AMin voltage 120V DC up to 377VDC. What capacitance do I need after the mains rectifier?

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 16, 2019, 09:51:21 pm
content: Quote from: SK_Caterpilar_SK on September 16, 2019, 06:49:57 pmAt it's simplest you can rearrange/modify the capacitor energy equation to solve this problem:C = [(2 * Pin) / (Vpeak2- Vtrough2)] * tdischargeWhere tdischarge is the period of half a line cycle (e.g. - 10ms in most of the world, 8.33ms in North America), Vpeak is the max voltage the capacitor charges to each half cycle and vtrough is the minimum voltage the capacitor discharges to each half cycle. A typical value for vtrough for full-wave rectified single-phase mains is 75% of Vpeak. Note that while the capacitor size is reduced as Vtrough is reduced, the peak current in the switch goes up. No free lunches and all that.For example, if you have 220VAC nominal mains and 500W input power then you only need 240uF to keep peak to peak ripple under 25%. That said, keep in mind that electrolytic capacitors have some of the loosest tolerances and lowest lifespans of any electronic component and you might find you need to use a lot more capacitance just to handle the ripple current and/or to achieve a reasonable life.EDIT - I haven't read all of this thread.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 16, 2019, 10:03:34 pm
content: So2x 56uF 450V and one 10uF low ESR all in parallel (perhaps a SMD high voltage cap to bypass it a little better. I dont know if that makes it any better but I expect it will)Max output power I expect is 70W peak 50W nominal.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 17, 2019, 12:31:26 am
content: One 100-220uF snap-in type will suffice. They have surprisingly excellent performance. Even a smaller value, give or take ratings (it may be conventional can style; always check the datasheet, in any case!).These flyback supplies use the same range, for 120V input (the one on the left has a 400V cap so should be able to run from a 240V input as well; or, I forget if the transistors were 600V+ rated, if they're only 250 or 400V, that's a bit of a problem with that).https://www.seventransistorlabs.com/Images/100WPowerSupplies.jpgSo at 240V only, even half capacitance (47-100uF) would be acceptable.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 17, 2019, 05:29:04 am
content: I'm using snap ins for the output filtration so I indeed plan on using snaps at the input side to keep the low profile look with them. Also I wanted two 56uF to give me total 112uF and another 10uF low impedance just to give it some extra security of it not failing in short order. The load would split evenly across the caps hopefully not stressing them too much.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 17, 2019, 11:26:11 am
content: Quote from: SK_Caterpilar_SK on September 16, 2019, 10:03:34 pm70W output max, so estimate about 100W input and I assume this is a flyback, but is it just for operation at your mains voltage (220VAC/50Hz) or "universal" (typically 90VAC to 260VAC or thereabouts), and so the input capacitance needs to be designed for the low-end of the voltage range?High frequency bypass of the input capacitance to a buck or flyback is always a good idea, but something like a 100nF film capacitor placed right across the power loop (e.g. - top of flyback primary and input ground) would be more appropriate; there's no help - and sometimes harm in the form of ringing - from placing the low-ESR bypass capacitor right next to the electrolytics doing the low-frequency ripple filtering and reservoir duty.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 17, 2019, 12:05:24 pm
content: It really won't matter because as long as the electrolytic is placed where the film bypass would be placed, it'll perform just as well. Bypass isn't critical on a flyback anyway, leakage inductance acts in series with the supply. The switch snubber is the only required low-inductance path.Tim

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 17, 2019, 12:59:56 pm
content: Quote from: T3sl4co1l on September 17, 2019, 12:05:24 pmBolded the key part; my point wasn't dissimilar, just more that 10uF of "low-ESR" (unspecified, but assumed film) capacitance directly in parallel with the bulk elkos located some distance away from the switching loop would be kind of a waste of money here.

author: m3vuv
author_rank: Super Contributor
timestamp: September 17, 2019, 02:36:01 pm
content: stick an hf transceiver near it if you think its noise free!!

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 17, 2019, 04:29:15 pm
content: Low ESR electrolitic (low impedance caps)

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 17, 2019, 10:37:37 pm
content: Alright this is how far i got. I dont have aux windings so I had no idea how to power the chip, so I decided to go with a pass tipe regulator, after all the worst it can get is 2W loss (5mA limited current draw).there will be a mains filter before the rectified, just externally. I have not chosen values for everything yet. There are two mosfets on the schematic (so I can either use TO247 or TO220).I dont have a snubber network yet. I dont know how to make one at all. And if its at all necessary. (Fsw 100kHz, VinDC 100V-400V and Ipk=2.55A)I have utilised all my dirty tricks there in the feedback to not burn the 431 in the instant the PSU is turned on.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 17, 2019, 10:54:50 pm
content: Also I have seen in many SMPS designs capacitors going from primary ground to the secondary ground (small capacitance high voltage rating cermaic caps). Rumor says its for noise reduction but I dont really know if it will be necessary. I can add them onto the PCB and during testing I can just leave try them and if it wont work nicely then not populate the places. I just dont know what capacitances to look for, and if its even necessary.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 18, 2019, 03:40:27 am
content: Snubber and Y-cap (GND-GND) depend on transformer characteristics.Ideally, a shielded transmission line transformer could be made, giving very little common mode noise, and a modest amount of leakage which may be tolerable without a snubber. This is not easily made, however: personally, I'd sit down and take about an hour to design such a thing, checking against available cores and bobbins to see how much winding area and wire length is possible, and therefore what impedance, and how much leakage inductance, I can get.But if you're just putting windings on a core, count on needing both, and common mode chokes.Typical snubber is just the drain pin into a diode into a capacitor to ground. The cap is relatively large (>= 10n?), so that the peak voltage gets clamped by it. This "boost" voltage is discharged into the DC+ supply with a power resistor.The capacitor can be DC+ referenced, if the DC+ bypass is nearby. This is often seen in commercial designs, since it's easier to lay out (the R and C are simply in parallel).Note that you want a TLVH431 or the like -- lower minimum current.Tim

author: mrjoda
author_rank: Regular Contributor
timestamp: September 18, 2019, 06:47:23 am
content: For bobbins and cores, check the semic trade (semic.cz) it is the best distributor for these things as i know in our countries.

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 18, 2019, 08:22:40 am
content: Thank you Tim for your reply.No the transformer is bought from coilcraft. Part number is HA4060. So far I did not make my own. Its been pre made for a different but similar purpose.The specs of the transformer are here. I will be slightly overdriving the transformer (2.5A Ipk instead of 2A)https://www.coilcraft.com/pdfs/ha4060.pdfIm not looking forward to wind my own transformers. I rather quote Coilcraft for something custom or the local manufacturer..Do I need a snubber network at all and if yes how do I design one ?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 18, 2019, 08:30:03 am
content: That transformer looks alright, 2.7uH is pretty typical and should be easy to snub.Look up SMPS circuits, you'll see how the snubber is wired. Typical values would be something like, UF4007, 10nF and 22kΩ.Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 18, 2019, 11:47:33 am
content: Also what are my options using a zenner clamp snubber? What re the drawbacks? Can I combine zenner clamping with the "traditional" way of snubbing? Is there even a point of doing that?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: September 18, 2019, 01:58:17 pm
content: RCD clamp snubber and zener clamp snubber are about as good. They are both better than RC damper, because the peak voltage is limited more rigidly.RCD rate (dV/dt) snubber is acceptable, and can provide reduced turn-off losses (in the transistor at least; with optimal values, the overall losses can actually be reduced slightly), and can be dimensioned to dampen the ringdown waveform (in DCM), but doesn't provide as good clamping.The only differences between RCD rate and peak snubbers is the RC time constant, and where the resistor is connected: in the rate snubber, the resistor is in parallel with the diode, and the RC time constant is small (a fraction of a cycle).Tim

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 18, 2019, 08:07:15 pm
content: So what would be the possibly best all arround solution. With the values you suggest and if possible a simplified schematic too.. Because at this point I have seen soo many variations that I have no idea which one is the correct one to use in my speciffic case.

author: MagicSmoker
author_rank: Super Contributor
timestamp: September 18, 2019, 09:25:56 pm
content: Quote from: SK_Caterpilar_SK on September 18, 2019, 08:07:15 pmWhat does your current design look like? Sampling a few random posts including the first one it seems that somewhere along the way this went from being a 12V input switcher of indeterminate type to an offline (aka mains-supplied) flyback.BTW - switchers are difficult, but you are doing much better at 17 than I was. Then again, you had to request datasheets by fax when I was 17, and the internet of the time were bulletin boards reached by 300bps modems... Good times...

author: SK_Caterpilar_SK
author_rank: Regular Contributor
timestamp: September 18, 2019, 10:12:18 pm
content: I do agree that the knowledge these days is more available than it was before. I respect you for keeping your work up even trough the difficulties of the age you were livving in. But with technology advancing and these amazing options, yet we are going downhill with intelligence. There is much less kids with actuall interests, and hobbies other than facbook, games, or perhaps drinking as a tred in my country (yeah kids of age 13 show up to the bar to drink beer or strong stuff).. I myself dont like alcohol at all, but I have to respect others choices. And I also was a big gamer nerd and to admit I still am with that one speciffic game that I have been playing for 7 years now xD..Anyways. The schematic is here I dont have speciffic values so far.I think I will take a short break from this project it has been bothering me for too long now. I will still be forum active but I will prioritise other projects. I plan a 20W AB 1980s style transistor amplifier which I have the board layout already done for. Also a lab bench powersupply utilising the good old LM723 (and its not your average schematic found on the internet, its actually better.) up to 60Vout and 5A max.There is a whole lot other things I have WIP, Im trying to keep it even.