High Voltage Bench Power Supply Design - Page 1
Forum section: electronics / beginners

author: iampoor
author_rank: Frequent Contributor
timestamp: March 27, 2018, 12:03:28 am
content: HelloI am working on building a high voltage bench power supply.I work with vacuum tubes, and have outgrown my Heathkit IP-17 power supply.My specifications for this supply are as follows-50-500v voltage output-0-200ma current output-Constant Current and Constant Voltage modes-Microcontroller based voltage/current meter and microcontroller based interface. (IE can be remotely programmed)I have selected the PSOC5 Development board (CY8CKIT-059) for my microcontroller-Can survive a shorted outputI want to base it on Rod Elliots project, but with a few upgrades/improvements. Here it ishttp://sound.whsites.net/project151.htmThis is my first discrete linear power supply design. And my first design with high power mosfets used in the linear region. I usually use BJT's or mosfets for switching purposes. Im sure I am not thinking of a few things correctly, so please feel free to make any suggestions or improvements. Right now this project is still in the brainstorming phase, so Im open to suggestions.https://imgur.com/a/3j5r4Here is my preliminary schematic, right now its just a bunch of filtering capacitors, mosfets, and a current sense resistor with an AD8479. I chose 2 SPW11N80C3FKSA1 N Channel MOSFETs in parallel, because they are a large package (To-247), Have a high Power dissipation, and can pass the required voltage/current. I have a 1 ohm resistor in series to limit current to each device, but Im not sure if this is the proper way to balance current between MOSFETS. This is just sort of a starting point. I am not set on using these MOSFETS, and I am open to other suggestions. I picked them because they fit my budget, and are commonly available, and seem to have the right specs.The real mystery of this design for me, is how to create the requisite gate drive voltages from my Microcontrollers DAC outputs. I would appreciate any suggestions or ideas and/or reading material. Most of the DIY High Voltage power supply designs I have seen use a similar arrangement to Rod Elliots design, a simple potentiometer feeding the Mosfet/Tube/BJT gate/Grid/Base.Ultimately I am taking on this project because I A. Need it and B. Need to fill many gaps in my knowledge and think this is a great way to do it. Thank you for reading this and I am looking forward to hearing from you.

author: james_s
author_rank: Super Contributor
timestamp: March 27, 2018, 12:22:42 am
content: What you're wanting to design is far from trivial, for a linear supply you could be dissipating >100 Watts in the pass device under conditions of max current into a relatively low voltage load. I would suggest not worrying about the microcontroller yet, get the basic linear regulator working solidly. I've used microcontroller based power supplies before and was not all that impressed, there are advantages of the good old analog approach.

author: iampoor
author_rank: Frequent Contributor
timestamp: March 27, 2018, 12:36:23 am
content: Quote from: james_s on March 27, 2018, 12:22:42 amYes, I am well aware of how this project might quickly turn into a big hassle. Ultimatly I am taking this on for the educational value. My first post was posted before I was finished, so I added some more information and I posted some of the initial designs I have seen and my take on it.The plan is to get a solid linear regulator working first. The microcontroller aspect is just something I would like to implement in the future and start brainstorming on. I have seen the simple analog approach, and mostly understand how it works, I just want a head start on how to design a circuit that can interface with my microcontroller, or if its even possible without it turning into a disaster.The few approachs I have personally started working on, were really quite poor!

author: Kleinstein
author_rank: Super Contributor
timestamp: March 27, 2018, 07:37:23 am
content: The interesting part is still missing: how to get the control signal to the gates.For the suggested specs I would go with the floating type regulator like HP used it in many of the older supplies. This uses a separate small transformer to power the regulator (and µC if used for control).The nice thing about this type of regulator is that it is very flexible in the voltage range. So one can first build it for a safe, lets say 20 or 30 V range and than later change a few resistors and the MOSFETs to get to 500 V. So the step to higher voltage would be only later, after the 30 V version working well.With a 100 W maximum power, I would consider using 2 transformer taps and than 2 MOSFETs in series for the control. There is a rather clever and simple way of doing this, a little like the class H/G audio amplifiers. This way the MOSFETs will only see about half the voltage, though it would be either one of the 2 MOSFETs to do the dissipation. Still it can save about half the heat sink.

author: oldway
author_rank: Super Contributor
timestamp: March 27, 2018, 10:49:17 am
content: This subject has already been debated here (12 pages!).projects/looking-for-yours-opinions hv-stabilized-power-supply"https://www.eevblog.com/forum/projects/looking-for-yours-opinions!-hv-stabilized-power-supply/"Are we going to start all over again?EDIT: URL corrected....still not working !!! Did not succeded to post the complete url, I don't know why....Tittle from this topic has been changed several times by topic starter...also 0-350V 0.2A Bench Power SupplyOk, working now....

author: iampoor
author_rank: Frequent Contributor
timestamp: March 27, 2018, 08:34:51 pm
content: Quote from: Kleinstein on March 27, 2018, 07:37:23 amThats exactly why I figured asking here was the right place! My transformer actually has dual High voltage wingdings and dual 6.3v low voltage windings.Do you have a recommended HP schematic to start with? I am only familiar with the HP6502B which is fully discrete.I was doing some more brainstorming today. What about using both windings of the transformer in series with there own rectifier,filtering, and MOSfet regulation. That way I can parallel parts with a good linear operating range like the IRF840. Any downsides to this approach?It seems too good to be true.Quote from: oldway on March 27, 2018, 10:49:17 amHi, this is not a repeat of that thread. The Original poster of that thrread apparently wanted everyone else to design something for him and it got extremely derailed. I am looking to improve my own design skills and make a useful piece of equiptment in the process. I dont really want to use tubes as the pass element because of space constraints.

author: oldway
author_rank: Super Contributor
timestamp: March 27, 2018, 10:26:53 pm
content: QuoteYour design skills ....you are kidding ?You already showed what is the level of your own design skills. (see your picture)....Nothing wrong to be a beginner, but a power supply 50-500V 0.2A is lethal....some forum don't even let you to open topics about such a dangerous project....It seems you did not read the advices about using MOSFET's in linear applications.....

author: Jwillis
author_rank: Super Contributor
timestamp: March 28, 2018, 12:06:12 am
content: Have you looked at the LR8.http://www.microchip.com/wwwproducts/en/LR8and you could use a IGBT like the FGL60N100BNTDhttp://www.farnell.com/datasheets/1725734.pdffor the little extra current .

author: iampoor
author_rank: Frequent Contributor
timestamp: March 28, 2018, 12:39:35 am
content: Quote from: oldway on March 27, 2018, 10:26:53 pmSee this is where the internet doesnt convey intent or experience well. I made it very clear that I have NEVER used Mosfets in linear applications and that my extremely simplified picture was the simplest starting point that I could think of. Im not going to put tons of effort into designing a schematic when I have never built the device before, or anything even close to it. Maybe that makes me an idiot, or maybe it means I have enough wisdom to not overstep my bounds. I want my ideas to be picked apart by those with more knowledge, as I am in this case, an absolute novice! I try to start things out as simply as possible, and then add pieces under reaching a desired outcome, because I otherwise get overwhelmed.However, that doesnt say a SINGLE thing about my level of experience with high voltage, safety, or construction techniques. I am a full time tech, and work on vacuum tube equipment every single day. I am very well aware of proper construction techniques, safety procedures, and design margins. But...I have NEVER designed a power supply before, and NEVER used mosfets in a linear application. Some things that may be common knowledge to others is completely lost on me, hence starting this thread and asking for advice. I am doing this to challenge myself and learn. If you would like to share some design expierence, I would really appreciate it, as you clearly have expierence in this area. If you are just going to approach me with a sour attitude, spend your time on other threads. I am not looking for someone to build a design for me, but I do need some hand holding, and am well aware of my own limitations.I posted that picture before reading any other information. As far as the other thread you linked, I am currently at page 7. Lots of crap to sort through in that thread.I am currently reading a Linear Tech application note on the SOA of Mosfets. Also readinghttp://www.ixys.com/Documents/Articles/Article_Linear_Power_MOSFETs.pdfLearning lots!Quote from: Jwillis on March 28, 2018, 12:06:12 amI havent seen those. Thank you very much! I will read the datasheets.

author: Jwillis
author_rank: Super Contributor
timestamp: March 28, 2018, 03:47:11 am
content: The pure MOSFET is not a really good choice for linear application .IGBTs are a kind of MOSFET BJT hybrid.Not say that there aren't MOSFETs designed to run in linear applications.The IXYS IXTN46N50L is one that I've been looking athttp://ixapps.ixys.com/datasheet/89945a33-9e28-4242-b812-008abd738156.pdf.The problem with ordinary MOSFETs is they get subjected to high thermal stress due to the simultaneous occurrence of high drain voltage and current, resulting in high power dissipation.Thermal hot spots occur in the silicon causing the devices to fail. Also though MOSFETs aren't typically subject to a "second break down" they get a sudden reduction in blocking-voltage capability followed by a loss of current control which is caused by the hots spots.This tends to be catastrophic to the MOSFET.The extended forward-bias safe operating area or FBSOA suppresses the positive feedback of electro-thermal instability on Linear MOSFETs.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 28, 2018, 04:51:13 am
content: Quote from: oldway on March 27, 2018, 10:26:53 pmOldway,Please cease and desist.You are disrupting the forum.Tim

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 28, 2018, 04:53:46 am
content: Quote from: Jwillis on March 28, 2018, 03:47:11 amWhat does IGBT have to do with this?Anyway, given the OP's background, I'm a bit surprised he's not going for a tube design right off the hop -- but if this should be a learning experience, introducing transistors, then linear-rated MOSFETs are a fine opportunity for many lessons.Tim

author: BravoV
author_rank: Super Contributor
timestamp: March 28, 2018, 04:55:29 am
content: Bookmarked this while ago, not 200mA though, only 10mA. And voltage mode only.Source ->EDN: Regulate a 0 to 500V, 10-mA power supply in a different wayNot sure if the current capability can be up scaled safely.

author: james_s
author_rank: Super Contributor
timestamp: March 28, 2018, 05:09:26 am
content: Well, safety is relative, but I see no particular issues with scaling up the current. Pass transistors can be ganged up with some care.

author: Jwillis
author_rank: Super Contributor
timestamp: March 28, 2018, 05:18:35 am
content: Quote from: T3sl4co1l on March 28, 2018, 04:53:46 amI apologize for my failure at composition .It was never my strong point.I meant that an IGBT could be used because the one I had linked earlier can be used in a linear application since the current requirements (200mA) fall within it's DC SOA.I was simply trying to help it a area that I'm currently experimenting with.I think that anyone who's seriously interested in electronics should take look at the vintage valves at least a little bit.Its quite fascinating.If in some way I have offended someone I sincerely apologize.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: March 28, 2018, 06:29:04 am
content: Ah. Yeah, IGBTs typically have very little DC SOA. BJTs as well, but as the above example at 10mA shows, they're not useless, just limited.Tim

author: Kleinstein
author_rank: Super Contributor
timestamp: March 29, 2018, 06:30:49 pm
content: IGBTs offer little advantage over MOSFETs - the IGBTs tend to be even worse when it comes to FBSOA. At high voltages BJTs also have a limited SOA and thus well chosen MOSFETs might still be better. All the semiconductor power stages tend to fail short if they fail. This can be a big problem for a high voltage power supply, as this would result in full output voltage - possibly enough to blow electrolytic caps in the circuit. So extra protection (e.g. a redundant emergency turn off or a crow bar) may be needed.With around 100 W or worst case power dissipation the heat sink makes up the size. If BJTs are used, it might take quite a few of those TO3 / TO247 high voltage transistors - so size might not be such a valid argument against tubes.If it really needs to be small, they way to go would be a switched mode regulator (to reduce the heat) with maybe an extra linear stage behind for fine adjust/filtering. However this makes it a rather complicated project and not for a beginner anyway.A simple regulator circuit to look at could be HY1803D - its a simple example of the floating regulator.

author: bd139
author_rank: Super Contributor
timestamp: March 29, 2018, 06:52:24 pm
content: I built an HV power suppy at university with similar capability. It’s not trivial. Mine did 400v at 1A.I actually ended up building a supply that used several transformers in series and relays switched in taps accordingly. The pass transistors (stack of 2n3055’s) dropped only a maximum of 80 volts at any point.This is actually similar to an HY1803D actually.

author: Sbampato12
author_rank: Regular Contributor
timestamp: March 29, 2018, 07:07:13 pm
content: Using another topology is allowed?Keithley HV digital power supply I've worked before, use a low voltage wave generator (20V~30V) to power a primary of a transformer with HV secondary. Then a voltage divider (high voltage) to sense the output voltage. That was a 5kV x 5mA or 10mA one. And after the secondary was a voltage multiplier (diodes and caps).

author: bd139
author_rank: Super Contributor
timestamp: March 29, 2018, 07:29:39 pm
content: That’s a neat topology. Makes sense.

author: BrianHG
author_rank: Super Contributor
timestamp: March 29, 2018, 08:57:50 pm
content: Quote from: Sbampato12 on March 29, 2018, 07:07:13 pmI like that idea. Use this guy:https://www.digikey.com/product-detail/en/wurth-electronics-inc/760895431/732-5062-ND/4692724Power a square wave from a power opamp at 100khz to the 2 12v+12v out (now being used as in), and put a bridge rectifier at the input pins (now power out) to get around 500v DC. Basically using this switching supply transformer in reverse, but, driving a linear varying square wave to make a flat DC output which will need only 0.1uf decoupling cap + safety fixed resistor load. With a linear amplitude square wave fed in this way, your output can go from 0v to 500v, and operate the device from a bench supply and be double isolated and no switching noise ripple since the output is always a 50/50 duty cycle full bridge rectified signal with no dead time.I would use 2 of those TI TDA-xxxx 100watt power audio opamps to drive the thing with an MCU making the varying the amplitude of the 100khz square wave (This is not PWM), monitoring the output voltage and current. The opamps would only operate at +/-24v and have short circuit current protection.However, being a very safe and near self-destruct proof design (except that high voltage can still kill), if memory serves, this design is above the OP's capabilities.

author: oldway
author_rank: Super Contributor
timestamp: March 30, 2018, 08:21:38 am
content: http://www.pmillett.com/HV_bench_supply.htmEDIT: see also HV power supply FUG MCP 140-650 0 - 650V 200mA.http://www.fug-elektronik.de/de/files/133000/MCP_Datenblatt.pdfhttp://www.fug-elektronik.de/en/products/medium-voltage/mcp.htmlEDIT 2: there is no specifications of ripple nor dynamic behaviour....Then, you could use a triac or SCR phase control .......Survive to a short circuit ? You can protect the primary of the transformer by a fuse or a circuit breaker.....only to blow a fuse will not "kill" your power supply.....A multimeter with a blown fuse is not "death"....

author: David Hess
author_rank: Super Contributor
timestamp: March 30, 2018, 07:02:05 pm
content: Quote from: Sbampato12 on March 29, 2018, 07:07:13 pmThe transformer moves the operating point on the power pass element SOA curve to a more favorable area so the secondary breakdown area is avoided. The trade off is higher noise, although not that much higher, and extra complexity. Some designs use the chopper transistors as the linear pass elements or drive the transformer with a sine wave instead of a chopped square wave.At 500 volts and 200 milliamps, I can see doing it either way but I suspect the chopper driven step-up transformer design is safer and less susceptible to catastrophic failure. For a high voltage linear pass element design, I would implement fold-back current limiting.

author: Jwillis
author_rank: Super Contributor
timestamp: March 31, 2018, 05:32:37 am
content: Switches are not the best idea for vacuum tube projects.If you get a leaking high frequency noise coming from the supply your tube amplifier and/or radio will be extremely noisy. Vacuum tube radios for instance can be noisy just from mains if you have switchers near them .I learned this ,with much frustration, from projects I have worked on.This is why going linear is the best choice for vacuum tube projects .MOSFETs that have no DC SOA do not respond well in linear applications.Even small currents can destroy them. You can DC bias them but that can be a bit more work. For the 200mA requirement, the IGBT is the least expensive ,easiest way to achieve the operating requirements of the OP. A proper Linear MOSFET would be a better idea but can be quite expensive. Although there are +500V transistor modules they to can also be very expensive.

author: David Hess
author_rank: Super Contributor
timestamp: March 31, 2018, 01:19:30 pm
content: Switches? Do you mean switching regulators?The described design using a transformer is an inverter and not a switching regulator. If hard switched, then the input and output current is continuous except during commutation. If driven with a high frequency sine wave, then it is no different than a line powered linear supply except for operating frequency. In both cases, noise is much lower than in a switching power supply and both types have been used in high voltage power supplies for tube equipment.Either would of course require output filtering but not nearly to the extent that a switching regulator would require.

author: iampoor
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:10:56 am
content: Quote from: T3sl4co1l on March 28, 2018, 04:53:46 amHi TimI would go for a tube design, but honestly, that would be the lazy approach for me. There are a few great design guides and published schematics, and I find that I really need projects to learn new things.I have designed Class A amplifiers, and simple BJT based circuits, but nothing that really takes much effort. Working through a couple of different approaches for this project has reminded me how much I still have to learn.Quote from: BravoV on March 28, 2018, 04:55:29 amI find this design really interesting. One of the things I noticed is that the voltage regulation is done using feedback, which I am assuming compensates the nonlinear photodiodes nicely. (Atleast I am assuming they are fairly nonlinear over the full range) I wonder that the transient response of this circuit is. I am almost tempted to build it just for fun.One idea I had that may make this circuit more useful (or perhaps just make me look like a fool), couldnt this circuit be improved by using a floating opamp to drive the base of a series pass element, and then use the photo diodes into a resistor as a current to voltage converter to adjust the reference voltage going into the opamp? Okay Im just thinking out loud and this may not make sense, but I might just draw up this idea and simulate it for fun.Quote from: T3sl4co1l on March 28, 2018, 06:29:04 amYes, just looked at the datasheet. Amazing how quickly the SOA falls off at higher voltages for that part.Quote from: Kleinstein on March 29, 2018, 06:30:49 pmYes, I am planning on having atleast 3 different protection mechanisims, fuse, crowbar, current limit. Of course some real world testing will be needed to see if the crowbar circuit is fast enough. Thankfully the enclosure I have for this is quite large, and I have a reasonable number of heatsinks on my shelf just for projects like these.Thank you.Quote from: bd139 on March 29, 2018, 06:52:24 pmVery cool! If I do go ahead with this project, I will have at a minimum two voltage ranges, getting 4 separate transformer taps wouldnt be a big deal either, thankfully transformers are affordable now a days. DO you have any pictures of your build? Sounds like a pretty cool project!

author: iampoor
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:15:03 am
content: Quote from: Sbampato12 on March 29, 2018, 07:07:13 pmQuote from: BrianHG on March 29, 2018, 08:57:50 pmQuote from: David Hess on March 30, 2018, 07:02:05 pmI am actually VERY interested in this topology. Either way, I am walking into unfamiliar terrority and am here to learn, so being above my design skills doesnt bother me too much. If noise is an issue, I can always follow the switching transformer with a linear regulator. The TDA3245 might be ideal for this application. Will be interesting to see how it responds to a short circuit...or for that matter, driving a transformer!http://www.ti.com/lit/ds/symlink/tpa3245.pdf

author: iampoor
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:23:32 am
content: Over the past few days, I have been reading about using MOSFETs as linear regulators, what to look for, and how to build and design floating regulators.I am posting a full list of the articles I have read, and a few parts that may be ideal for this project. Of course, the idea of using an inverter topology is also fascinating to me. Maybe inverter, followed by linear regulator? Only time will tell.MosfetsIXTH2N150Lhttps://www.mouser.com/datasheet/2/205/Viewer-766443.pdfIRFPG50https://www.mouser.com/ds/2/427/91254-104428.pdfFrom what I can tell, a Few IRFPG50s in parrallel would be a good option, but I would love to hear from the experts if I am missing something obvious. :-)http://www.ixys.com/Documents/Articles/Article_Linear_Power_MOSFETs.pdfThis is the article that turned me on to those parts, they use them for a programmable resistive load at 600v and 2amps in Figure 5Also read these artciles.https://assets.nexperia.com/documents/application-note/AN11599.pdfhttp://www.powerguru.org/how-to-make-linear-mode-work/http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.459.3616&rep=rep1&type=pdfAnd here is an example circuit I have been working through, high voltage regulator with a floating opamp (I think I am pretty close to understanding how all the parts in this circuit work)https://www.neurochrome.com/high-voltage-regulator/Why am I posting all of this here? Well I would like more reading material suggestions, and I dont want to forget all these links!

author: iampoor
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:31:59 am
content: Quote from: oldway on March 30, 2018, 08:21:38 amThank you.Acceptable output ripple is still TBD. I only work with vacuum tube circuits (mostly guitar amps) and most of these amps have a few v Peak to peak on the B+ supply.As far as dynamic behavior goes, I would rather design it to be fairly slow and not overshoot. Most of the amps I work on have pretty poor power supply designs to begin with.I really need to get to the point where I start building and simulating circuits before I can decide on some numbers, but I can confidently say that my requirements are far below being "laboratory grade". Those fug power supplies are beautiful!

author: qno
author_rank: Frequent Contributor
timestamp: April 01, 2018, 10:39:52 am
content: Hi all,I have a Delta Elektronika E0300-0.1.0-300 V 0..100 mA.It is a Dutch psu. Based ond the same circuit the older HP powersupplies worked.Schematics are online.They are regulary offered online.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: April 01, 2018, 10:53:31 am
content: Ah good; as one professor I had, would say of his aggressively scoped (but generously curved) tests: "an opportunity to excel..."Quote from: iampoor on April 01, 2018, 10:10:56 amActually it's... well, a couple of things:1. Optoisolators tend to be more nonlinear due to the LEDs, actually! This is most important to phototransistor (but I'd say not photodarlington) and photodiode (small signal) kinds. (There's a dual-photodiode version out there, which can be used to linearize the circuit. Photodiode current is sensed, with an opamp on each side, by keeping the diode's terminal voltage at zero, or under some reverse bias, so only the photocurrent matters.)2. But in this case, the diodes are photovoltaic, so you have the V(I) characteristic of the diode, in parallel with the photocurrent. (That's why a solar panel's peak power point is at ~80% of OCV, rather than 50% like a pure resistive source would be.)3. That doesn't really matter anyway, because they're sourcing current into a B-E junction. Except not quite just that, because the emitter resistor adds some offset (which linearizes the BJT's voltage-to-current curve, but probably makes the LED-to-current curve worse because of #2!). Ooh, good improvement here: simply return the diodes to the emitter, not to the output -- the current limiting transistor can still shunt base current to do its job, while the diodes hardly need to source any voltage at all, keeping them more linear. Nice.4. But even that doesn't matter, as long as the gain is modestly stable (within a factor of 2, say -- which is probably true here), and the op-amp gain is large (which it is, >10k). Feedback accounts for that error, so that the DC error is largely due to the op-amp, not the isolation. (At AC, where the op-amp's gain is small, the nonlinearity will be exaggerated. You want to design the passive output filtering (bypass) to take over at this point.)QuoteThe above, more or less addresses this case -- LED and diode nonlinearity dominate. But also like I said, and, as long as you're taking the trouble to float op-amps up there: you can spare another op-amp, as a current-to-voltage converter (transresistance amplifier; which is better than just a resistor, because it holds its input voltage constant), and use a dual-photodiode isolator. The LED in the isolator illuminates a diode on the LED side, and on the isolated side; they get proportionate illumination, and are matched devices, so as long as the diode environments are matched (that's the point of using the op-amp on either side), the output and input voltages will match.Actually that implies needing two op-amps on the high side, but you can use a single amp to convert input current to output current (precision current mirror), or to output voltage (which will appear as a negative output -- arrange the feedback divider accordingly).I guess the biggest change for you, will be: understanding DC coupling. AC coupled amps are simple, you slap them together however as needed. No need to worry about matching up bias voltages. Downside: global NFB encounters an LF pole for every coupling cap or transformer in the loop. You can get motorboating, very easily.The most basic and powerful method, is to match up the extremes of voltage and current ranges, for each stage.Everything takes an input voltage and current range, and everything can deliver an output voltage and current range.To match up the output and input ranges between stages, adjust the ranges with voltage dividers, bias resistors and such. To avoid inconvenient bias supplies or attenuation ratios (voltage dividers are signal dividers, too), choose the type of stage based on the ranges they are capable of. (Don't forget you have complementary parts available, too!) Usually, large resistor ratios and dummy level-shifter stages are completely avoidable!You should only need level shifting, when you're stuck with a device of given range. Example, a +/-15V op-amp, and a +60/0V emitter follower. You need to add 15V to the op-amp output, to make a +30/0V range, then 2x gain to get 60V output. You'd design with somewhat looser values (like +12V offset, and 2.5x gain), to account for op-amp saturation voltage limitations (V_OL), and component tolerances.What you wouldn't do, is slap in a transistor and call it done. This shows up all too often -- it's ugly, and it's easy to see why, when you look at things in this way. Say you run a series resistor from op-amp to BJT base (emitter grounded), and a pull-up resistor on the collector (which goes to the output). The op-amp's +/-15V range is poorly utilized: below -7V, the B-E junction is avalanching (damaging the transistor), and the op-amp has to slew its output a full ~16V before anything interesting happens (this causes many microseconds of saturation recovery -- messy!). As the op-amp output rises above Vbe, the transistor conducts, exponentially -- meaning, gain varies exponentially too, making the loop gain unstable. Depending on hFE and resistor values, the top 5 or 10V of the op-amp range may be useless as well, holding the transistor in saturation (incurring saturation recovery in the other direction as well!).Yet the fix is painfully simple! Add an emitter degeneration resistor (to VEE, rather than GND), and now the op-amp's full voltage range is usable, giving a collector current proportional to input voltage. We still have a Vbe vs. V_OL problem, so we might offset the emitter voltage upward slightly, with a large resistor from GND or VCC to emitter. We don't need a series base resistor, but we also don't want the full +15V range at the base, because the collector can only pull down as low; we want a 0V output range, so let's divide the op-amp output by 2, towards VEE, so it's a 0/-15V range instead.And just like that, with the addition of four resistors, we've transformed a messy hack into a well designed level shifter!(Do follow along this discussion with pen and paper -- I know how easy it is to miss things in a text description!)Tim

author: oldway
author_rank: Super Contributor
timestamp: April 01, 2018, 11:34:22 am
content: Quote from: iampoor on April 01, 2018, 10:31:59 amIn the 70's, I designed and manufactured tube amplifiers for guitar and hi-fi.My bench power supply was very simple: in fact, since none of the amplifiers had a regulated power supply, I thought that a regulated power supply did not make any sense because it would not behave like the definitive power supply of the amplifier....This is particulary important for B and AB class amplifiers where current consume vary with output power.How was my HV power supply? I used a multi-tap transformer, a multi-position rotary switch, an AC side fuse, a bridge of BY100 diodes, electrolytic capacitors, an inductor, other electrolytic condensers ...I had 2 positive outputs, one before the inductor (high ripple), another after the inductor (low ripple).The rotary switch could select the dc output voltage from 200 to 450Vdc approximately in jumps of about 50V .....On front panel, I had a 500V analog voltmeter and a 250 mA analog milliammeter.To discharge the electrolytic capacitors, there was a power bleeder resistance.For safety, I had a bipolar switch that cut off the AC power to the diode bridge and shorted the output with a low-value power resistor.There was also a main switch, a "on" neon light and a high-voltage neon light.The power supply also had 2 outputs 6.3V 5A and a negative bias output adjustable by a 2W potentiometer from 0 to -80V approximately. (unregulated)

author: oldway
author_rank: Super Contributor
timestamp: April 01, 2018, 11:52:40 am
content: Let us remember the hybrid solution, Tube pass element driven by an optocoupler and compatible with µc control.....EDIT: NB: current limit is only a safety feature if max current is limited to 30 mA or lower. (see schematic 30 mA HV power supply)

author: Cliff Matthews
author_rank: Unknown
timestamp: April 01, 2018, 01:01:43 pm
content: Those 4004's need a little boost.. but we get the idea..better to use 4007's

author: oldway
author_rank: Super Contributor
timestamp: April 01, 2018, 01:34:21 pm
content: Quote from: Cliff Matthews on April 01, 2018, 01:01:43 pmThat's right, I used symbols of EAGLE "as is", I should have to change the name of the components....But if you look at the thread where I posted these schematics, you will understand that it was only to show the principle of working.This has not been copied from Internet, they are my own schematics.

author: BrianHG
author_rank: Super Contributor
timestamp: April 01, 2018, 01:56:36 pm
content: Quote from: iampoor on April 01, 2018, 10:15:03 amRemember, you are driving that transformer with a 100khz signal. A class D amplifier will only do audio output frequencies and it requires too many filter inductors and it's too low voltage.Use 1 of these opamps:https://www.digikey.com/product-detail/en/texas-instruments/OPA541AP/OPA541AP-ND/251157< needs more supply voltage, 10 amps max, 3 amps at 30v SOA with 85 degree casehttps://www.digikey.com/product-detail/en/texas-instruments/OPA549T/OPA549T-ND/307860< better output swing, but, 8 amps max, around 2 amps at 30v SOA with 85 degree caseSince it is linear & 1.6mhz bandwidth & 10 amps max, you can feed it's output directly into the digikey switching transformer I mentioned. You will need a good heatsink. For testing, if you have a function generator with adjustable output, 1 or 2 hefty 30v-50v 5amp bench supply, I would buy the opamp and transformer and test what you can do with wiring a home brew test design. As for the output of the transformer, you can use just a huge resistor banks to test maximum voltage under load & probe the output, but, it will be AC of course. Get a 1kv bridge rectifier + an 0.1uf X cap as DC filter make it DC. If you achieve you max voltage and current you want, then, we can take a look at using a microcontroller to feed the op-amp setting and regulating voltage and current. You may also add digital display and control here.As for the class D amp, try to find a Chinese board using the same chip in mono high power mode, with full 100Khz support, buy it and the transformer and try it that way. Note you might be able to run or find a transformer at 50Khz or 25Khz to make it easier, but, your output AC-DC filter on the high voltage side gets a larger and larger capacitor as the frequency goes down. This doesn't mean anything above 1-10uf, but, it means if you short your output, you will get that current surge held in a 10uf capacitor at 500v.Remember, the switching transformer has 1 high voltage winding, 1 sense winding (do not use), and multiple matched low voltage windings. You will select whether to wire the low voltage windings in parallel or serial depending on the op-amp voltage range. Serial winding with higher voltage means less loss and less current through your system, but, you will need an amp with higher voltage output.

author: David Hess
author_rank: Super Contributor
timestamp: April 01, 2018, 04:43:55 pm
content: Quote from: iampoor on April 01, 2018, 10:15:03 amTektronix used this inverter transformer configuration in their oscilloscope power supplies starting with the 22xx series up through the 24xx series at power levels up to about 100 watts.Figure 26 on page 12 ofLinear Technology application note 12(1) shows a modern switching variation of this circuit which produces a 0 to 500 volt 200 milliamp output. (2) For lower noise, the input buck switching regulator can be replaced with a linear regulator. The output inductor shown in the schematic is for filtering and is *not* a buck inductor.Since the transformer provides a fixed step-up ratio, current limiting could be implemented on the primary side. Voltage regulation can also be implemented on the primary side which is what Tektronix did in most cases so the output then becomes completely isolated which will be advantageous in some applications.The second example below shows the same idea from application note 18 with a linear regulator but power is limited by dissipation of the linear regulator. Note the primary side current limiting.(1) If this link still works by the time you get it. Analog Devices is busy erasing everything Linear Technology published and discontinuing their products.(2) I had completely forgotten that Jim Williams produced a 200 milliamp version of this circuit. I was looking for the 0 to 1000 volt reference he designed.

author: BrianHG
author_rank: Super Contributor
timestamp: April 01, 2018, 05:20:05 pm
content: Hmmm, you can replace the LT1010 + fet in that design with a logic level mosfet.Though the idea of using a charged center tap on a transformer, raising it's VCC to gain voltage at the output is nice, it doe consume more current.

author: oldway
author_rank: Super Contributor
timestamp: April 01, 2018, 06:40:41 pm
content: Yes, it's a good technology.Let's hope that the transformer and the inductors are still available on the market.

author: David Hess
author_rank: Super Contributor
timestamp: April 01, 2018, 06:43:55 pm
content: Quote from: BrianHG on April 01, 2018, 05:20:05 pmI thought that aspect of the design was a little weird. The LT1010 is an analog power buffer so this is like driving the switching transistors with an operational amplifier albeit a fast and high current one; I think an PNP/NPN buffer would have been better but maybe Williams wanted to take advantage of the LT1010's built in current limiting. The 74C74 high voltage CMOS flip-flop used to generate the 12 volt switching waveforms can only marginally drive the power MOSFETs without help.Since low noise is a design objective, I would change that whole section to provide non-overlapping drive like Jim Williams suggests in the text. There are lots of ways to do this but an inexpensive SG3525A switching regulator controller could directly drive the power MOSFETs with controlled deadtime and has its own oscillator in one chip.QuoteThe current is increased but the lower operating voltage means the transistors avoid the secondary breakdown area of their safe operating limit curve.

author: BrianHG
author_rank: Super Contributor
timestamp: April 01, 2018, 07:06:20 pm
content: LOL, that design is using an Audio Tube Amplifier 100 watt transformer which no longer exists.I used to use that center-tap trick on a 60hz transformer as a 12v-120v inverter, but, it sank a ton of current for no reason just powering up.Feeding just the ends of the transformer with a push/pull amplifier, like the 10 amp, +/-40v op-amps I listed, wouldn't sink and waste all that current and those opamps have built in programmable current limiting capability. Your power supply would be something like a PIC mcu with 2 DACs, 1 feeding an adjustable amplitude square or sine wave into the opamp -/+ input & the second DAC would DC feed the current limiter input pin on the op-amp programming the maximum output current.That's your whole supply right there. 1 MCU with 2 DAC's, 10 amp opamp, 1:20 transformer (you will target +/-25v into transformer, use around +/-35v as opamp power supply), DC bridge rectifier on output with optional filter. Also, optional voltage fed back into an ADC on the MCU to keep voltage exactly where you want it under varying loads. +++ A good heatsink!Obviously, you can replace the MCU with a 20-100Khz oscillator and 2 pots to set voltage and current.