Another kit: All-discrete power supply - Page 1
Forum section: electronics / projects

author: c4757p
author_rank: Super Contributor
timestamp: January 02, 2014, 09:10:39 pm
content: While I am still working on my function generator kit (well, after my week-long break), I had originally planned to put together multiple kits, all in the same "How Analog Works" style. The damn FG is taking too long; I'm going to simultaneously put together a much simpler one, so that I will actually havesomethingcompleted before I grow oldThis is a power supply (0-30V 500mA) made entirely from discrete components, but designed to have the line and load regulation of a "proper", opamp-controlled PSU. The regulation loop is fully differential with optional, external sense terminals (obviously not too necessary at 500mA, but they are used to cancel out any internal resistance including through an ammeter). Mostly SMD again, but unlike the FG there aren't as many parts, so it's all 0805. (Unfortunately SOT-363 is a bit tricky to solder and I needed three of them. Inexpensive matched pairs are a bit hard to find.)I have tested the circuit, but using hand-matched transistor pairs without good thermal coupling, as I do not have the specified parts. Line regulation was 1mV on 30V over an input voltage range from 35 to 45V (0.03%), load regulation was about the same from 0 to 500mA. Once I order PCBs, I will fully characterize the circuit for line and load regulation, temperature coefficient and transient response with the correct parts installed, and will make a probably futile attempt at measuring the output noise with the equipment I have on hand...The total BOM cost for the control PCB is $10 sourcing all parts from Mouser in decent-quality versions; I will be able to cut probably 20% from this by sourcing general-purpose transistors and resistors elsewhere. This does not include an enclosure, a transformer, a heat sink, the contents of the front panel (pots, meter, meter switch, banana jacks, power switch, power indicator), and the contents of the rear panel (mains connector, fuse holder and fuse).Modification for power greater than 500mA is fairly simple and will be addressed in the assembly instructions, but will require significant heat sinking (40W for 1A, 80W for 2A).I will order PCBs tonight; more info to follow after testing them.P.S. It looks like KiCad's PDF export is fixed now. Previously, I had to export all greyscale PostScript and convert to PDF. If anybody has problems opening the schematic, please let me know.P.P.S. I'm going to work on the documentation tonight, so if anybody has any "how does this part work?" questions, please wait until I post that. If you have any "you're an idiot and this will never work" comments, feel free to post them now before I spend too much time documenting a brainfartP.P.P.S. If anybody has any good info on temperature-compensating a Zener, I'm all ears. I used a 6.2V diode + 1N4148, which seemed like a good combination according to the datasheets. There appears to have been a series of compensated Zeners at one point, but I can't find any now. I'm not going to use a bandgap reference because that violates the "all-discrete" design pattern here. I'm nottooworried about temperature compensation, as that's more of a long-term drift property, at least once the unit warms up, but Iammaking an effort to keep it from being dreadful. It's not a precision instrument, but I do like a power supply that starts up to the same voltage I set it to yesterday.P.P.P.P.S. This is the most P.S.'s I've ever used.

author: cellularmitosis
author_rank: Unknown
timestamp: January 02, 2014, 09:32:52 pm
content: Excellent! I've been following / reading the archived threads about the LM317 approaches as well as op-amp / pass-transistor approaches, and this makes a perfect third companion.Been hacking on an LM317-based supply myself as of late. Fun!

author: calexanian
author_rank: Super Contributor
timestamp: January 02, 2014, 10:32:27 pm
content: Looks like fun. Some good learning to be had there. There are many people i encounter that claim to be engineers who do not even know how a conventional AB discrete amplifier works. I like to see discreet kits as it really teaches how a circuit works. Sure you could use a couple of LM317's but you will not learn anything.

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 02, 2014, 10:58:22 pm
content: c4757p, throw in a discrete triac pre-regulator

author: c4757p
author_rank: Super Contributor
timestamp: January 02, 2014, 11:18:27 pm
content: An intriguing idea, but definitely more complicated than I want for this. The function generator is my ALL THE FEATURES!!! project

author: Kappes Buur
author_rank: Regular Contributor
timestamp: January 02, 2014, 11:45:25 pm
content: Quote from: c4757p on January 02, 2014, 09:10:39 pmI cannot open the pdf file. All I get is this:

author: Monkeh
author_rank: Super Contributor
timestamp: January 02, 2014, 11:48:02 pm
content: Quote from: cellularmitosis on January 02, 2014, 09:32:52 pmWatch out for those cheap 10-turn pots. They're seriously fragile.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 12:11:39 am
content: Quote from: Kappes Buur on January 02, 2014, 11:45:25 pmThat looks like a problem on your end, or with the forum software. The .pdf extension has been stripped. Try saving it and then adding the extension manually.

author: liquibyte
author_rank: Frequent Contributor
timestamp: January 03, 2014, 12:27:31 am
content: Here you go, have a png.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 12:34:32 am
content: Glad I decided to put together a SPICE sim from the schematic, to include with the docs. Just noticed I swapped the wires to the voltage reference at some point while rearranging the schematic... D'oh!

author: Unknown
author_rank: Unknown
timestamp: January 03, 2014, 12:42:01 am
content: Quote from: Kappes Buur on January 02, 2014, 11:45:25 pmProblem with your browser. Something isn't configured for opening PDF's, or incorrectly configured.

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: January 03, 2014, 12:47:08 am
content: Dave found a temperature compensated zener in his EDC MV106 calibrator teardown (#210)...Microsemi 1N821-1seems to be the current version. Mouser doesn't seem to source from Microsemi at all, and digikey doesn't stock it; I guess everyone uses the reference ICs now? avnet lists it as in stock for qty 1, but looks like it'd be a pretty big increase to your $10 discrete BOM! (judging from digikey's price.)

author: johnwa
author_rank: Frequent Contributor
timestamp: January 03, 2014, 01:20:14 am
content: Quote from: Kappes Buur on January 02, 2014, 11:45:25 pmIt looks like the server is giving a Content-Type: of application/octet-stream for all types of attachments. I am not sure to what extent this is a problem - it sort of acts as a suggestion that the browser saves the file instead of opening it immediately, though in the end it depends on how your browser is configured. Perhaps I will mention it to Dave.

author: cellularmitosis
author_rank: Unknown
timestamp: January 03, 2014, 01:24:27 am
content: Quote from: Monkeh on January 02, 2014, 11:48:02 pmThanks for the heads-up, I was wondering why they were priced "too good to be true"...Do you know what the common failure mode is? e.g. should I expect the wiper to eventually go open-circuit?

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 01:25:00 am
content: Oh freaking great. The KiCad "I'm not going to open your PCB file, and I'm not going to give a meaningful error message. Segfault! Fuck you!!" bug strikes again. Well, the PCB will have to wait until I can get this sorted out. Hopefully tonight.I'll attach a SPICE sim and new schematic soon; I made a couple changes to fix things I didn't notice on the bench.

author: Monkeh
author_rank: Super Contributor
timestamp: January 03, 2014, 01:30:35 am
content: Quote from: cellularmitosis on January 03, 2014, 01:24:27 amThe glue on the terminal bar fails and the hilariously thin wire within proceeds to break.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 03, 2014, 01:43:59 am
content: Quote from: c4757p on January 03, 2014, 01:25:00 amMawha ha ha ha, ... oops, sorry, shouldn't laugh. As far as I know, the Kicad files are all ASCII based, so you can go in there with your favourite text editor and remove, change, comment-out the offending bit. Caveat: I'm not responsible for any bits of PCB you delete, destroy or otherwise disconnect.QuoteSomething that has been tweeking my pots (as t'were), and I can't quite make my mind up, but: You have the load connect to the collector of the "output amplifier", so the loop gain of the voltage control is defined by the load - which is unpredictable - wouldn't it be better to use a voltage-follower output stage?.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 01:50:42 am
content: It would be more stability-friendly in theory, that is certain. To be honest, I don't remember why I chose that topology... I haven't had any problems with it at all, though, and I've tested it with large capacitive and inductive loads as well as resistive. It is a fairly common arrangement.I will consider changing it, though, especially considering that the kit is supposed to be instructional. "Eh, it works for me!" isn't exactly good engineering!Edit: Theory != practice. A quick swap plus reconfiguration of the error amplifier has made averyunhappy control loop that seems to chew up and spit out most compensation topologies I can think of.. I spent enough time farting with the loop today - I don't really feel like changing it in the name of "good practice" when I've got a working circuit.Quote from: Andy Watson on January 03, 2014, 01:43:59 amSeems to be an error in loading the file, not saving. I think the file is fine. Though, I will try the old "binary search" method to figure out which part it doesn't like (for the uninitiated, load only half the file, then the other half, then descend into the bad half, narrowing down which section works and which does not).

author: Andy Watson
author_rank: Super Contributor
timestamp: January 03, 2014, 02:29:28 am
content: Quote from: c4757p on January 03, 2014, 01:50:42 amI agree, that's why I said I couldn't make my mind up. An "n" of 1 working devices outstrips an "n" of 0 theoretical devices! Although, I am still weary of putting some of the specification into the "user" space; you never know what the user is going to hang on to the output!QuoteIf i remember correctly (and I could be remembering a totally different program), the parser doesn't have much error detection. If something does not conform to the "format", it just runs off the end of the file looking for the appropriate terminator string, hence seg fault on a missing comma, or too many commas etc..

author: Andy Watson
author_rank: Super Contributor
timestamp: January 03, 2014, 02:58:17 am
content: Oh and, ... at the risk of returning the original topic, full marks for presenting a ground-up power supply design from first principles. I'm getting a bit P'd-off with seeing yet another method of forcing a LM317 to do what it was never intended to do. I'm not anti LM317, but, right place, right time?

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 02:59:11 am
content: Quote from: Andy Watson on January 03, 2014, 02:29:28 amI spent a few days writing a library generator for KiCad - most of my libs are auto-generated - and I will have to correct you here. It doesn't haveanygoddamn error correction.....OK, maybe a little.....SPICE simulation here. It's a little bit messy; I'm not done with it. But it works.Note on the SPICE sim: There is a software instability that does not appear to exist in real life. Some load conditions (including, 100% of the time, the SPICE active load/current sink) cause the circuit to oscillate at 5 MHz for about 2ms during startup. I see no startup instabilities in real life, and it quickly stabilizes. The solution is not to run ".tran startup" under these conditions.Changes made:1) Startup sequencing. The main rails come alive before the dedicated bias rail for the current limit amplifier, meaning that for a few ms, the output is unlimited. I added Q14, Q15, R25, R26, and R13, which override the control loop until the bias rail is up.2) Active load on the differential amplifier. With 2N3904 there was enough DC gain for good load regulation with a resistive load, and the lower AC gain made the loop easier to stabilize. With the PMP4201Y (could just be the model - I don't have one on hand) the line regulation goes out to 0.1%. WIth an active load I am getting 0.002% in simulation - real life, I'm sure, won't be quite that good. This also means no bias trimpot is necessary.3) Changed the voltage loop compensation. It stabilizes differently with the active load, of course. Annoyingly, this also contributes to the line ripple rejection... It's pretty decent now, though I'm considering sitting down to a cup of coffee and calculator and designing a compensation network with a steeper edge around 120 Hz.The reference designators should match the schematic, unless I missed something, though I haven't posted the updated KiCad schematic The SPICE one should do for now. I'll post the schematic along with the PCB after I finish fighting with KiCad.Shh... don't tell anyone I packed the models in the zip file. IIRC you're not supposed to distribute themDon't forget to probeacrossthe load to measure the voltage. Thoseinductorsoutput leads both have resistance!

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 03:05:14 am
content: Quote from: cellularmitosis on January 03, 2014, 01:24:27 amYou shouldalwaysexpect wipers to go open circuit, because they doall the time. Always design your circuit to do something safe if this happens.Speaking of which, my voltage pot. Er.... thanks for bringing that up.

author: calexanian
author_rank: Super Contributor
timestamp: January 03, 2014, 03:21:32 am
content: Quote from: Monkeh on January 03, 2014, 01:30:35 amThose Bourns knock off ones. Bonens i think they have written on them. Garbage.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 04:13:21 am
content: Found it! It saved the file wrong. Yet another case of "KiCad developers can't handle symbols in names".It saved an invalid net ID for every copper pour that was tied to V- or V+.They are supposed to be integers >= zero. The fact that it segfaults if it encounters a -1 makes me suspect something very, very dirty in the net code. Like, parsing the numbers and then shoving them directly up the ass of an array subscript without a bound check.Think I'll file a bug report. I can't get it to save the file wrong againbut it consistently segfaults on -1, which isverybad.If anyone has that problem, look for any instances of (net -1) in the PCB file, and just remove the whole key-value pair including parentheses. That'll leave the pours unassigned, and you can just edit them and reassign them.Edit.... nope.... it doesn't even always choke on (net -1)...God, they put the shittiest coders they can possibly find on parser duty. I was going to be nice and put together a minimal test case, but I guess they can just dig through my whole 3000-line PCB file.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 03, 2014, 04:33:06 am
content: Quote from: c4757p on January 03, 2014, 04:13:21 amI've only reverse engineered the bits that I needed to know about but what did stand out was the total inconsistency in string handling. Some strings are quoted; some are not. Some strings have special identifiers at the start, some...who knows? It doesn't seem to matter! If you've managed to embed a special token in the middle of an unquoted string - you're stuffed

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 04:39:04 am
content: Yep. It seems to me that they have some logic in place to determine whether quoting is necessary. It appears to be choking on V+ and V-, which presumably it doesn't like because of the symbols.Why the hellwould you not just quotegoddamn everything?? Do they pay royalties to the HDD manufacturers for any bits used to encode quotation marks? Freaking hell...New PCB and schematic attached. I'll wait to order the PCBs until tomorrow morning in case I think of something else I missed....oh look, I did. Again:Quote from: c4757p on January 03, 2014, 03:05:14 am

author: Monkeh
author_rank: Super Contributor
timestamp: January 03, 2014, 05:10:12 am
content: Quote from: calexanian on January 03, 2014, 03:21:32 amThe pot in question is not a Bourns knockoff.

author: calexanian
author_rank: Super Contributor
timestamp: January 03, 2014, 05:21:18 am
content: Bonens....Chinese names..... Still the best one i have found are "Lusty" batteries.

author: BravoV
author_rank: Super Contributor
timestamp: January 03, 2014, 07:53:12 am
content: Subscribed.Chris, what is the targeted performance for this little gem of yours ? May be some preliminary/draft specifications ?

author: peter.mitchell
author_rank: Super Contributor
timestamp: January 03, 2014, 11:27:35 am
content: Quote from: BravoV on January 03, 2014, 07:53:12 amDon't catch fire.Quote from: c4757p on January 02, 2014, 09:10:39 pmI guess this is close enough for the moment.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 11:34:04 am
content: Yes.(As a matter of fact, this is why I don't presently have more test data.... I stupidly set my prototype down on a couple wire trimmings, stupidly didn't notice until I smelled magic smoke - I was doing a load test and so the current limit on the input was high - and now I have a very tightly packed perfboard with many crispy transistors, including two tediously matched pairs. I couldn't be bothered to rebuild for a prototype that doesn't even have the same part numbers as the final circuit. I'll just wait for it.)

author: BravoV
author_rank: Super Contributor
timestamp: January 03, 2014, 11:36:27 am
content: Quote from: peter.mitchell on January 03, 2014, 11:27:35 amOk, fair enough, meanwhile, back to stalk&lurk mode.

author: sorin
author_rank: Frequent Contributor
timestamp: January 03, 2014, 12:10:00 pm
content: Quote from: Kappes Buur on January 02, 2014, 11:45:25 pmDelete Cookies and will work

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 01:08:42 pm
content: Quote from: Andy Watson on January 03, 2014, 01:43:59 amBack to this.The reason I couldn't get it to work is.... wait for this..........After reconfiguring the error amp for the loss of one inverting stage, I never moved the compensation network. The negative-feedback compensation became positive feedback.I was having one hell of a stupid day yesterday.It's actually significantly better like this. Not just stable in practice, but in theory too. And the line ripple rejection has improved as well, not depending on the feedback loop anymore. Thank you for the suggestion. Just had to sleep on itNew SPICE, schem and PCB coming soon.People... friends don't let friends design circuits in a hurry.

author: megajocke
author_rank: Regular Contributor
timestamp: January 03, 2014, 03:17:58 pm
content: Very nice project!How about using this kind of recitifer circuit so you'd be able to use a single secondary transformer? The voltage might be a bit higher than you wanted though, but you could regulate it down (maybe using a simple zener + resistor shunt regulator?).PS. Is your Kicad symbol library self-made? It looksreallynice, almost like it's not Kicad!PPS. What is J4 for? Looks like connecting it to the transformer winding would cause a short circuit.

author: megajocke
author_rank: Regular Contributor
timestamp: January 03, 2014, 03:26:13 pm
content: Maybe something like this?

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 03:56:21 pm
content: Quote from: megajocke on January 03, 2014, 03:17:58 pmThat would work, but the voltage would bewaytoo high. As in, 20V too high. I only need 2V there, up to 4 or 5. The intent was to just add an auxiliary winding by hand to the transformer - should only require a few turns of insulated wire between the existing, sealed bobbin and the core, for roughly 3Vrms.Another possibility would be to drop those volts in a couple diodes, but I didn't want to waste headroom because the specs put me right around a couple common transformer voltages.QuoteYup. Thank you!QuoteSomewhat bodgy, though useful, versatility in transformer selection. You can connect a single 24-28V winding across J3 and J5 with a bridge rectifier, or place two 1N4004 diodes in the footprint instead and connect a 49-56V center-tapped winding across all three.

author: AndersAnd
author_rank: Frequent Contributor
timestamp: January 03, 2014, 04:06:37 pm
content: Quote from: c4757p on January 03, 2014, 12:11:39 amThis happens to all (or most?) PDF-files I have downloaded from this forum. Just gets named "downlaod (1)" or whatever number unused. Very annoying to have to rename the PDF files.Only happens to PDF-files uploaded to this forum. No problem with from other sites.(Using Chrome browser on Win7 atm., but can't remember if it happens in FF and IE too).

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 04:08:27 pm
content: Linux FTW! Doesn't give a damn what the extension is, if it looks like a PDF and quacks like a PDF it is a PDF.New schematic and PCB attached; I'll add the SPICE stuff after I add a loop stability analysis to it.

author: AndersAnd
author_rank: Frequent Contributor
timestamp: January 03, 2014, 04:11:11 pm
content: Sigh, I fear this topic will turn this topic into yet another Linux vs. Win debate.

author: GeoffS
author_rank: Unknown
timestamp: January 03, 2014, 04:13:39 pm
content: Quote from: AndersAnd on January 03, 2014, 04:11:11 pmNo it won't. I won't let it and I'm a Linux bigot from way back

author: calexanian
author_rank: Super Contributor
timestamp: January 03, 2014, 04:15:21 pm
content: Quote from: megajocke on January 03, 2014, 03:26:13 pmYou need that resistor in series with that zener or the zener will release its smoke.

author: c4757p
author_rank: Super Contributor
timestamp: January 03, 2014, 04:20:29 pm
content: Quote from: AndersAnd on January 03, 2014, 04:11:11 pmI will be very cross with anyone who does that.I have no strong feelings about Linux vs Windows. I use Linux because I haven't used Windows seriously in at least six or seven years and I'm no longer comfortable with it. I've no interest in learning another system just to say I have. But I don't care whatyouuse. Both have their advantages and disadvantages.Not that it wouldn't be just a result of my thread derailment karma to have this turn into an OS war.Oh damn. I'm not uploading a new schematic until the SPICE is done, but add a 12k resistor in parallel with C7 (for open-circuit wiper failsafe)

author: megajocke
author_rank: Regular Contributor
timestamp: January 03, 2014, 11:43:29 pm
content: Quote from: calexanian on January 03, 2014, 04:15:21 pmThere _is_ a resistor in there, just not in the place one might expect.But sure, for such a low voltage, not that many extra turns are required on the transformer.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 01:56:07 am
content: After spending some time checking and re-checking the PCB, I sent it off. I do somewhat regret not including dummy footprints for layout-dependent frequency compensation, but I don't foresee that being an issue. A few minor, cosmetic changes were made.I'm not going to prepare a full SPICE sim with stability analysis. That's going a good bit outside the scope of the kit; it does take some intuition to interpret the results and I'm not going to teach a whole lesson on stability and control loops here. I don't feel qualified to write that explanation.And besides, it's an old-fashioned all-transistor power supply that I designed in the first place without SPICE. Kind of doesn't feel right.Here's the beginning of the manual, with two sections of the Theory of Operation completed. There's a good bit of Theory of Design in there too. I'll just edit this post to update it as I go. Feel free to help me proofread

author: Galaxyrise
author_rank: Frequent Contributor
timestamp: January 04, 2014, 08:35:17 am
content: Quote from: c4757p on January 04, 2014, 01:56:07 amFrom reading this, I think I'm probably the target audience. Thanks for putting something like this together!Figure 1.1: I found the green line confusing, how it can connect to the black side of the top rectifier without turning it green. You do explain later that you consider the circuit having two grounds, but that wasn't apparent to me from the label "local ground". Even knowing what they mean now, I think I'd be just as happy without the green lines in that diagram.Figure 1.2: I found the top spans much clearer than the bottom spans. Perhaps use the same pattern, so have a 32.4V and a >= 4.6V instead of two overlapping spans? Also, Q1/Q2 are missing a part number but everything else is labelled.I'm not sure I agree with "there is no one ground"; I can call anything the ground that I want! I'm sure you told SPICE that one net was the one groundI get what you mean, though, there's a variable voltage gap between the two parts of the circuit.I was surprised by the C6 charging math. I recognize the basic capacitor charging formula, but expected VMax would be 2.4, (and thus a charge time of 5RC.) I played around in LTSpice a bit, and I think I get what's happening. But your formula is still just a close approximation, right? The LTSpice curves diverge around 85% charged.I had trouble following the tempco of the zener. First, you list the tempco as 800ppm (which, as I read the datasheet, is optimistic. 27.4 - 33.4mV/C translates to 830 - 1012ppm.) But then that's followed with "1.6% in either direction over the specified range" and I thought you meant +-800ppm, but that didn't work out (and zeners don't have a +- tempco anyway.) Perhaps, "-1.6% at 5C and +1.6% at 45C" would have been easier for me to digest.I liked the explanation of the constant current source. Maybe add where the value for R1 comes from?nitsPage "1": "front-panel Voltage potentiometer". I don't think voltage should be capitalized there.Page "1": the next paragraph starts with an awkward sentence. Perhaps: "This potentiometer feeds a differential voltage into the error amplifier, which compares it to the differential voltage sensed from the output."

author: codeboy2k
author_rank: Super Contributor
timestamp: January 04, 2014, 12:13:22 pm
content: Quote from: megajocke on January 03, 2014, 11:43:29 pmYep. +1 to c4757p for posting a V+ referenced schematic on an Australian forumI hear that's how they keep the electrons from falling out over there

author: Bored@Work
author_rank: Super Contributor
timestamp: January 04, 2014, 01:19:01 pm
content: Quote from: c4757p on January 04, 2014, 01:56:07 amFigure 1.2: DC voltage has direction, so all the blue voltage arrows should be uni-directional (one arrow head), not bi-directional. Direction is from higher to lower potential, so the arrow head should be at the more negative end.Also, I would give all of the voltages quantity names like V1 = ..., V2 = ... This would make it much easier to refer to them later in the text. E.g. nstead ofQuoteQuoteorQuoteDepending on the direction of the arrows.Quantities and units:The notation you use for the quantities and units is inconsistent. Your tax dollar helped to produce this documenthttp://physics.nist.gov/cuu/pdf/sp811.pdfand the short versionhttp://www.nist.gov/pml/wmd/metric/upload/SP-811-2008-Checklist-Reviewing-Manuscripts.pdfThey describe how it is done (although I don't agree with the idea of using the period as the decimal separator, but well, it is the US, you know ...)Examples:* The equation at the start of page 3. The math is done without the units, this is an big no-no. And suddenly the result is in ms.* You also have some magic equations like 40m/330 inline in the text. Well, 40 meters divided by 330 is 12.12 cm* Taking the last two paragraph as an example:QuoteAlso you should double check your error calculation. I am too lazy to do it now, but error propagation calculation doesn't work by just adding percentages.

author: dannyf
author_rank: Super Contributor
timestamp: January 04, 2014, 02:21:56 pm
content: QuoteIt is nice to design a discrete power supply for the sake of designing a discrete power supply. It is nicer if it can beat a lowly 3-terminal regulator in performance.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 02:39:55 pm
content: Oh wow, thanks to both Galaxyrise and B@W, looks like you really spend some time reading through it.Galaxyrise:- Yup, no green lines would be better. I agree, they are misleading.- I'll add an explanation rather than changing the voltage spans. They're like that for a reason: I'm showing the differential voltages thatmatter: Vbias->VCC (which biases current sources), VEE->V+ (which supplies the regulator), the total V- ->V+ span (which shows the possible output voltage span, as I will address in a section I haven't yet written), and the V+->Vbias headroom (which proves that the current sources won't ever saturate). All others are incidental.- I did indeed pick a net as ground in SPICE, but it was inconvenient. Many voltages made more sense relative to a different rail. I used V+ as ground because it ruined fewer nice numbers than any other. That's pretty common in discrete-transistor circuits: "ground" is whatever an individual transistor sees at its emitter.- C6 charging math: 3.5V is Vmax because until the Zener diode begins to conduct, it's not really there. The capacitor charges as if 2.4V doesn't exist and it's just charging towards the rail. The Zener will suddenly clamp it at 2.4V. I'll add a note to this effect.- No comment on the tempco yet - from reading both you and B@W, it looks like I've got to spend a bit of time rechecking that. There probably is something wrong with it. I'll dig into it a bit later - just got up for morning coffee and have to do other things first.....- You're right, I should explain R1. Added.nits:- Front-panel Voltage potentiometer: Capitalization is correct, and I will add quotation marks as well. It's not a "voltage potentiometer", all potentiometers are (potentiometer!!!!). It's a "Voltage" potentiometer, as in, that is its label.- Yep, that sentence is awful.Bored@Work:- You are absolutely correct about DC voltage needing a direction label. I was careless to just assume the "positive up" convention. I will change the arrows to all point to negative, but I will also add + and - labels, as arrow direction convention can confuse beginners.- I wasn't sure whether I wanted to label quantities like that. It does make it easier to refer to them, and it is of course standard practice in academic papers and such, but in my experience the uninitiated can find that it makes the text seem denser and harder to follow. I'm still not sure. I'll have to consider this one.- I really like that NIST checklist. Definitely going to add that to my collection. And use it here, of course- Ew... magic equations and math without units. Did I really do that?I'm so sorry for anyone who had to see that. Fixed!- And as mentioned above, I think you are right about the error calculation. I'll go over that again a bit later today.

author: megajocke
author_rank: Regular Contributor
timestamp: January 04, 2014, 03:56:35 pm
content: Do arrows indicating voltage have the arrowhead at the positive end or at the negative end? I've actually seen both used! It seems most people prefer the negative end to have the arrow (matching the electric field direction), and I guess maybe the other convention comes from thinking about vectors or something. I much prefer +- indications rather than arrowheads to avoid the ambiguity, and this was also the way they did it in all courses at my university (in Sweden).But I also have one thing I was thinking about concerning circuit operation. With your current configuration, depending on at what point in the AC cycle the power switch is turned on, you might be without the half-wave rectified bias voltage for a full half cycle. The time constant for charging the main filter cap would be around 3 ms give or take (assuming a 30 V, 30 VA, 10% regulation transformer), so it seems the main supply has time to come up to almost full voltage in that half cycle, activating the regulator without activating neither the current limiter nor delay circuit.It also looks like the current limiter and startup delay circuit will stop working on mains brownout.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 04:19:58 pm
content: Good points.I may have to change the bias supply to full-wave then. Grr.... I just ordered PCBs.......I don't think brownout will be an issue. The "delay" circuit should activate whenever the bias supply sinks under 2.4V, and it barely requires any voltage (just Vbe IIRC, though I can't get the schematic to load on my phone). Should take a pretty severe brownout. Maybe I will increase the bias rail voltage spec to reduce the possibility.It may still cause an issue at very severe brownouts.Perhaps it will be better to derive the bias supply from a couple diode drops.Looks like this will get a Rev B. Oh well, at least the main circuitry can be tested on the A boards just fine except for that.

author: sync
author_rank: Frequent Contributor
timestamp: January 04, 2014, 04:46:07 pm
content: Is it possible to change the current sensing to the V+ side and get rid of the bias supply?

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 05:44:40 pm
content: Yes, but the current sense loop was a bit grouchy, so I would rather not restructure it and have to play around with stability. I don't want to have to do a Rev C after finding that B is unstableOTOH it would be more elegant. Hmm... elegant vs. already works.

author: edavid
author_rank: Super Contributor
timestamp: January 04, 2014, 06:40:41 pm
content: Quote from: c4757p on January 02, 2014, 09:10:39 pm1N823 is readily available, although a bit expensive @ $3.There's no reason why you can't build a discrete bandgap reference though...

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 06:43:49 pm
content: I don't know enough about semiconductor physics to really be qualified to explain how it works, and also, from what I understand about them it would be quite tricky to get good performance. The 6.2V Zener + standard diode seems to work well.OK, I've changed the the power section. The bias supply is now made from diode drops. This version seems to lack all the problems found above, including brownout issues (the bias supply is activewaybefore there are enough VBE's across C1 to start giving output).I haven't made any changes that can't be bodged onto the Rev A board, so I will thoroughly test the circuit like that before ordering Rev B. That gives me plenty of time to figure out what else I messed up...Also: R18 and R19 go down to 1k5 and 390.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 08:37:31 pm
content: Damn. Analog panel meters are freaking expensive. I think you're going to have to settle for a - *shudder* -digitalmeter.I'll try to set it up so an analog one can be used instead, but I'm not going to specify one.

author: megajocke
author_rank: Regular Contributor
timestamp: January 04, 2014, 08:51:57 pm
content: What are your goals for the current limiter?Passing the load current through the diodes establishing the current limit reference would create some funny effects I think. The diodes heat up and the current limit lowers, for example.How about instead changing the way the output darlington is biased? You could put in something requiring biasing current from the upper rail to activate the pulldown resistor on the base. I guess it could be done with the same number of transistors as the previous circuit.

author: liquibyte
author_rank: Frequent Contributor
timestamp: January 04, 2014, 08:56:25 pm
content: Quote from: c4757p on January 04, 2014, 08:37:31 pmTry looking over at Jameco. Digikey and Mouser are ridiculous for those. I don't visit Newark.

author: Thor-Arne
author_rank: Unknown
timestamp: January 04, 2014, 09:03:28 pm
content: Quote from: c4757p on January 04, 2014, 08:37:31 pmYou can also try AliExpress if you don't mind the delivery time, likethis store.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 09:16:38 pm
content: I think I can do a custom 4-digit meter for $6. That's nearly on par with the cheapo ones you can buy (none of which seem quite right for the application). A PIC16F677 ($1.44) to digitize and drive the display, an LTC-4627JR LED display ($1.96), a TL431 ($0.31), perhaps a transistor or two and a small handful of passives. $1 for the PCB, and that's $4.71 plus assorted costs. I'll probably bring back the hand-wound aux winding to allow this to float....Quote from: Thor-Arne on January 04, 2014, 09:03:28 pmEven better! Clearly I suck at AliExpress. I missed that completely. Good prices! I don't see any of the type I was looking for (the old-fashioned 10/50/100uA meters meant for use with external circuitry). Am I wrong in thinking that if I open up one ofthese, I'll be able to remove a series resistor to convert it? I'll probably have to open them anyway, to put in a custom scale.Speaking of AliExpress, how wary should I be of small semiconductors? MMBT3904, 3906, MMBD4148? They've recently jumped in price on Mouser etc. from "sensible" to "hell no"...Quote from: megajocke on January 04, 2014, 08:51:57 pmYep. I should have seen that already... Simple solution though - use three 4001 for the drop, and then two 4148 plus a resistor as the reference.I don't want to restructure the current loop, as I said, because it works well already and it was tricky to make it play nice.

author: Monkeh
author_rank: Super Contributor
timestamp: January 04, 2014, 10:03:34 pm
content: Quote from: c4757p on January 04, 2014, 09:16:38 pmYou can probably buy one for that. Speak to Franky.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 10:19:22 pm
content: I think I'm going back to an analog meter. Fits the style of the design better, and Thor-Arne found some for me for a decent price. I'll still have to pop them open and add a custom scale, though, unless I can somehow find one labeled both 0-35V and 0-600mA...

author: edavid
author_rank: Super Contributor
timestamp: January 04, 2014, 10:27:17 pm
content: Quote from: c4757p on January 04, 2014, 09:16:38 pmIf you are ordering small quantities and you are OK with random Chinese parts, Tayda is pretty good.If you are ordering a reasonable quantity, you can do just as well with a US distributor. Arrow is usually cheapest, but their website is frustrating. Avnet's is a little easier to deal with. Do you know about findchips.com and octopart.com?

author: Thor-Arne
author_rank: Unknown
timestamp: January 04, 2014, 10:52:54 pm
content: Quote from: c4757p on January 04, 2014, 10:19:22 pmI popped open a91C4 5Vi have here. There is indeed a series resistor, don't know about the other models though.Soldering isn't that great, but who complaints at that price.Edit: urlI also tested it on 5.0012V, varies a little with the angle, but not much.

author: c4757p
author_rank: Super Contributor
timestamp: January 04, 2014, 11:08:34 pm
content: Who thought it was a good idea to put the null screw on the inside?I'll take my chances with the one I said, that one has it in the right place. Thank you for the picture, though. I'm sure they're all pretty similar.

author: Thor-Arne
author_rank: Unknown
timestamp: January 04, 2014, 11:18:32 pm
content: Quote from: c4757p on January 04, 2014, 11:08:34 pmIt is probably the same inside.You can ask it they're able to get the exact ones you are looking for, they're pretty easy to deal with. Just use simple languange.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 03:01:19 am
content: I'm not going to bother, as I need a custom scale (and don't need enough units to have them do it for me). Might as well snip out a resistor while I've got it open to change the scale plate.I just ordered a couple, and I'm going to order some parts tonight.Just so I can do some planning: can I get a PM from anybody who is likely interested in buying one? You aren't committing, just helping me out a bit. To make this clear: this is a "most parts" kit. You must provide the heavy parts (enclosure, heat sink and transformer) as I simply cannot afford to buy these items in any quantity and ship them. I've tried to keep the design relatively versatile in terms of what can be used, so if you have access to any junk parts they may be of use.- Transformer: 28V, 30V, 56VCT, or 60VCT, 20VA min, 30VA preferred; recommended: Hammond 187D28.- Heat sink: Any TO-220-compatible heat sink that can take 18W.Two notes on power:1) I am beginning to seriously consider either a tap-switcher or thyristor preregulator, so that heat sink requirement may go down.2) If I don't do #1, I am going to prepare a version (this just requires changing component values, nothing else) with a 20V maximum instead of 30V. That cuts the power requirements (both transformer and heat sink) quite a bit.The anticipated cost of either version will be $25, including PCB, electronic parts, front and back panel parts, and a printed manual.Edit: #1is out. That's a bit much. Again, out of scope. But I will add a thermal cutoff.

author: Bored@Work
author_rank: Super Contributor
timestamp: January 05, 2014, 11:14:49 am
content: I would delay the decision about the meter once you have done your homework about the error calculations.What's the point of ruining a (potential) good precision with an imprecise meter?OrWhat's the point of adding a precise meter to a power supply that is (hopefully not) staggering all over the place like a drunken sailor?

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 03:28:44 pm
content: Quote from: c4757p on January 04, 2014, 09:16:38 pmI was thinking along the lines of putting a switch in series with the resistor that turns on the output transistor (collector resistor of the common emitter amplifier after the voltage regulator differential pair), and to have this switch require current from a current source on the upper rail to turn on.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 03:32:16 pm
content: Maybe I'm being dense, but I don't see how that will work for current limiting. It sounds more like an alternate version of the startup delay circuit, which I no longer need due to the new power input arrangement (bias railalwaysstarts first).Also, I do not want a current limit that overrides the voltage error amp, causing it to saturate, because I don't want the voltage to overshoot when the load is removed. By pulling on the feedback instead, the voltage amp is still in control and running at full speed.Quote from: Bored@Work on January 05, 2014, 11:14:49 amI'm not going to use a very precise meter because they are expensive and it's not really necessary. For example, my Power Designs TP343A has specs that are even better than these, and it has the same old-style analog meters and is just fine. Most of the time you don't need to set the voltage to the millivolt, and if you do, you can just test with a voltmeter. If it's that critical you should be doing that anyway, unless you're using a really nice, newer, software-controlled PSU with a million self-tests.Like I said before (though I might not have made it clear): I want line and load regulation to be excellent, because those help isolate the effects of the PSU from the effects of the DUT. One of my cheaper PSUs, for instance, has rather poor line regulation, and if I'm powering a circuit and measuring with a 4.5- or 5.5-digit meter, I can see the readings fluctuate as nearby loads on the mains cycle.I'm not so concerned with long-term drift and things like that. I want the voltage to stay constant during the hour while you are using it; I don't really need it to stay constant tomorrow. But as I added, that would certainly be a nice bonus.Of course, if the PSU is staggering like a drunken sailor it needs to be fixed, not matched to a crappier meterBy the way, I fixed everything you mentioned in the text, except the error calculation (didn't have time to do that). I'm going to work on that now, and then I'll post an update. Thank you, again, for taking the time to go through it for me.

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 03:46:36 pm
content: Quote from: c4757p on January 05, 2014, 03:32:16 pmYes, that's what I meant - as an alternative if you wanted to keep the separate bias winding. But if you feel you can live with a somewhat higher droupout voltage caused by the diode string it seems like a good solution, and won't require modifications to the transformer.If you are interested in some more unusual operating conditions you might want to look at what happens if the output current is externally forced higher than the current limit (throught the output diode) or if the voltage is forced higher than the voltage limit. This could happen if supplies/batteries are put in series or parallell respectively.It might also be interesting to look at what happens if the output is connected to a voltage source, e.g. a battery, while the power is off. Such operating conditions make many power supplies unhappy, so having survival as a requirement might be overkill.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 04:36:32 pm
content: Thanks for the suggestion. I thought of these things, but forgot a necessary part to make them work properly: a reverse protection diode across the output transistor.If the output current is forced high through the diode, the sense resistor won't see it (as usual - those diodes are often connected right across the jacks). I may add a slow-blow fuse inline with the output to prevent blowing the diode up. Those low-voltage inline fuse holders used in automotive audio apps are very inexpensive.Forcing the output high saturates the amplifier, but doesn't do any damage if I add the reverse protection diode.Connecting to a voltage source while powered down also is harmless with the addition of a diode; the external voltage source will actually power the control circuitry, which will just saturate as usual like when the voltage is forced high. Anything up to 50V will not damage the circuitry (as it is designed for that much in case of excessive mains voltage feeding the transformer - which reminds me, I need a MOV on the input - and R1 must change to 22k, and a 4148 must be added in series with Q12/Q13 to keep the 50V from feeding back up to VEE), and anything over about 48V will trip the TVS diode on the output.

author: BravoV
author_rank: Super Contributor
timestamp: January 05, 2014, 04:40:26 pm
content: Quote from: c4757p on January 05, 2014, 03:32:16 pmThis, is exactly what I wanted to hear, and confirms that I'm not subscribing the wrong thread.Way to go Chris.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 04:41:39 pm
content: Did I say a magic word?

author: kxenos
author_rank: Frequent Contributor
timestamp: January 05, 2014, 04:56:52 pm
content: Excellent project Chris! And your schematic is very professional! Way to go!

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 07:22:43 pm
content: I was worried that if the output is connected to a voltage source while power is off (referring to your latest schematic) C2 will stay uncharged because of the diode string D1,D5,D6, and the voltage reference which is powered from the output will together with the voltage sense resistors provide current which can flow through the BC-diodes of the voltage error amplifier input devices, breaking down the BE-diode of Q7 (and maybe Q16A-B too) in reverse. The current is limited though so this would amount to degradation of the transistors at most.If the output is connected to a voltage source with a higher voltage than the setpoint with AC power on, if I'm not mistaken Q7 will try to saturate and pull quite high current (looks like you have enough base drive to get a few hundreds of milliamps) in reverse through the BE diodes of Q8 and Q9. Something would probably let out the magic smoke almost instantaneously.It also looks like the current source for the current error amplifier, Q11, will start to saturate if the output voltage starts to reverse. Collector-base voltage is about 0 V when the output voltage is 0 V, right? But maybe this is not a problem? As long as you keep the externally forced current below the rating of the supply the current throuh the output transistor can't exceed the design value anyway.Were you simulating this in LTspice? Something to look out for is that the standard transistor models don't model reverse breakdown of the BE-diode.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 07:37:49 pm
content: New schematic.Added the thermal cutoff. The thermistor is a Vishay NTCLE100E3104JB0 - 13.4k at 75°C. That puts 0.64V on Q17, switching on the two-transistor "thyristor". You must power-cycle to reset (I think that's a good thing. Not only does it keep the transistor from getting hot, but it keeps you from leaving a heavy load attached, walking away, and letting it slowly cook itself as it shuts off and comes back on repeatedly.)The current flow is a bit unconventional - I noticed that if something were to go wrong in the current control feedback path, the voltage error amp could saturate high and actually risk damaging a few parts. I added resistors and clamp diodes (R9 and D4, which have already been there, and R33 and D10) to prevent this problem, and then took advantage of them in the thermal cutoff to save parts, byintentionallysaturating the amplifier. When the Q17/Q18 thyristor switches on, the feedback path is slammed to VEE, sending the output high (this is thenegativeoutput, so "high" means "no output" here). Q5A saturates, drawing base current through Q7, through D4 and over to the thyristor - but not before it goes through a warning annunciator LED, DS1. Because this also saturates Q7, the output transistor's B-E junction would be reverse biased. I added R33 to limit current and D10 to clamp the voltage.I also changed the output transistor to a TIP105 Darlington, which has a protection diode built-in, eliminates Q8 from the PCB (moving some of the power dissipation off the PCB and onto the heatsink), and is a bit cheaper too.Quote from: megajocke on January 05, 2014, 07:22:43 pmSolved, I believe, by adding a bypass diode (D11) antiparallel to the diode string.QuoteYup, found this problem already (as mentioned above). Q7 no longer commits murder-suicide when it saturates.Speaking of high voltages, an interesting problem that does exist in SPICE butnotin real life is that a forced voltage higher than the voltage across C2 will blow up D11 in SPICE, but not in real life, because in real life that voltage comes through a rectifier.QuoteCorrect.QuoteYes, I finally gave in to the temptation of SPICE, and it bit me. I've been checking manually for B-E reverse bias but missed that one.Time to go back to pen and paper.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 05, 2014, 07:52:57 pm
content: How do you plan on selling your kits Chris? Own web, tindie, eBay, crowd, etc?I personally feel you could make decent money with the following, kits might be your calling!- PS- Electronic load- FG- Maybe a .01% DC voltage referenceA single FET programmable uC based electronic load could be a big hit IMO. Dual pushable rotary encoder, on/off button and a 16x2 display with battery test/AH mode.Mmmmmmmmmmmmm

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 08:06:58 pm
content: TBH I don't know. I'm doing this actively on the forum to gauge interest and polish them a bit. And because I can't afford to sell more than a few in the beginning - hopefully there are enough people who know me well enough here to at least know that I'm not a complete idiot and probably not a scammerand can deal with my bullshit a bit as I try to handle making and selling the first few while barely being able to afford it......I'd probably blow all the money I'd make on a voltage reference on a *calibrated* (with cert) voltmeter for testing..... I have decent confidence in my 3468A because its cal only expired a couple years ago, it's been treated well and matches everything I've tested it against, but I wouldn't want to do references without at least attempting traceable verification of their accuracy. And there are plenty of them out there. And it would make an awful kit, as most kit builders wouldn't have the equipment to verify its accuracy.One thing I've considered making for myself: a computer-controlled device tester - basically a "curve tracer" without the logic. Just a couple low-power voltage/current sources and ADC channels that can be programmed to do pretty much whatever you want. Think that could be successful? It would be somewhat simple to do, and people love scriptable shit.Just have to say the word "Python"...Thoughts?How should I proceed once the kit is "complete" and I've sold a few privately here?And by the way - caught another problem (I'm not an idiot, I swear, I just tend to post "finished" schematics too early) - R15 and R33 do not provide enough base current at high output currents for particularly pathetic specimens of TIP105. Unfortunately, simply lowering their value does rather increase the power dissipation in the "forced output voltage" case, where D10 conducts, so I may need to use 1/2W resistors there. That condition can put up to 50V across each of them, as the output falls to -50V and Q7's collector sits at 0 (48.somethingV is the maximum guaranteed clamping potential of the TVS). That, or I'll just add another 3906 and make it a "triple Darlington".

author: SeanB
author_rank: Super Contributor
timestamp: January 05, 2014, 08:24:27 pm
content: Just make it a selection for high gain on both darlington transistor devices. Solves that issue.I had some fun trying to explain to people that Hfe is a variable value with current, I was selecting some devices not caring about the power device ( it had a gain of under 3 at the current it was handling at best) but was selecting the driver devices based on saturation voltage instead using a small test jig which ran them at close to the in circuit operating conditions. A lot failed to meet the specs I desired, but then again I did have a big box of 2N2219A's to go through so enough were in the spec. They had a failure mode where they unsoldered themselves from the leads. Not helped by the heatsink being poor and running next to a 150W lamp that they were driving.

author: blackdog
author_rank: Frequent Contributor
timestamp: January 05, 2014, 08:26:27 pm
content: Hi c4757pJust some 2 cent remarks...Why don't you use a reference diode like the 1n821 series?C3 wil not do much, because the internal resistens of the zener is less than 20 Ohms.Mayby its better to make C4 bigger to get lower noise?What is the what is the purpose of d10, R33?The problem is not the low gain of the TIP105, but your design (for better gain and dissipation use a TIP147).Remember the risistence between base and emittor of such a transitor is normaly below 8K.I Think your design wil be verry onstable, because of the high resistance values in your design, this creates a lot of LAG...Thermal cutoff, use a Clickson to cutoff the basedrive of Q9.My advice, do not start with the circuitboard for the circuit have been extensively tested on dynamic stability.Kind regarts,Blackdog

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 08:34:52 pm
content: How about using a diode instead of R33? Then you wouldn't need D10 either.Putting in D11 should work, but an alternative might be to put a small signal diode in series with the positive supply to the voltage error amplifier, similar to the way the current error amplifier has one. (edit: But this is not compatible with the circuit where the reference for the current source is separate from the diode string)If you want the supply to be able to stand a sudden application of a voltage source to the output when AC power is off, there is a risk the current error amplifier will be damaged by the current pulse charging C1 (and C2 if using D11) flowing through R21. Initially the whole (forced) output voltage will drop over R21 and especially if RV4 is set to zero the input to the differential pair will overload and cause reverse EB-diode breakdown in Q12A.I guess it could be fixed by adding some resistance in series with the base of Q12B together with a small signal diode.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 08:48:22 pm
content: Quote from: SeanB on January 05, 2014, 08:24:27 pmI could, but I'd rather not have to bin parts (and be stuck with a pile of shitty ones!). Maybe I'll search a bit more for one with higher minimum gain. Such asQuote from: blackdog on January 05, 2014, 08:26:27 pmEdit: Wait.... that doesn't have higher gain! 1000 vs 2000...QuoteEngineering rule of thumb: X depends on Y, for X and Y in {all properties of everything}...blackdog: I'm not using a 1N821 or similar because they're expensive. This is sufficient. You're correct about C3 not doing much, but it does do one thing: ramps the reference at startup, which helps keep the output shut down while the system stabilizes. C4 is just to shunt off RFI picked up in the wires to RV2.D10, R33 prevent Q9 from being reverse biased if Q7 saturates.Quote from: blackdog on January 05, 2014, 08:26:27 pmYou are correct, and after a bit more testing I added 10nF across C10. The lag caused by the feedback resistors hasn't been a problem (at 18k Thevenin, the impedance of the feedback path is not extremely high, and the amplifier is not very quick). I will admit that there are theoretically better ways to design the feedback loop, but I have thoroughly tested the circuit and have not been able to destabilize it at all. I'll test the PCB more thoroughly when I get it, before I send off revision B.Quote from: megajocke on January 05, 2014, 08:34:52 pmDiode instead of R33 sounds good - I will do that. And you're right about D11 - as the current amp already has one, I'd rather be consistent. At a glance, it looks like I can save a diode and just use D5 for that.I'll add protection to Q12 as well.

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 08:57:54 pm
content: Another thing I was thinking of was R(Q9B). I was thinking that it probably doesn't do much difference whether you put it close to the transistor or at the far end of the wire. Is placing it close to the transistor base based on having actual problems when it was far away, theory, simulation or just hearsay? I see it as a common suggestion but I can't find any theoretical backing unless the wires are insanely long (or the transistor is insanely fast). As long as it swamps the inductance of the base wiring up to the fTof the transistor or so it should be okay.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 09:02:15 pm
content: It serves two purposes: dampening parasitic oscillation of the transistor, and low-pass filtering (with the base capacitance) any RFI picked up in the wire. The latter requires it to beafterthat RFI pickup. Now that the transistor is an emitter follower, it's probably totally unnecessary.I wanted it there when the transistorscollectorwas at the output because of the large voltage gain. Perhaps I will remove it.

author: SeanB
author_rank: Super Contributor
timestamp: January 05, 2014, 09:20:20 pm
content: Losing parts is what eBay was invented for. Sell them as selected for gain, all falling within a band. Base/gate damping resistors are better close to the device, especially for Mosfets.

author: megajocke
author_rank: Regular Contributor
timestamp: January 05, 2014, 09:25:35 pm
content: Parasitic oscillation is quite likely in an emitter follower so I'd probably want to keep the option. In this case maybe the ESR of the electrolytic capacitors is enough to damp it, but I would not count on it...The "problem" with emitter followers is that if the load is capacitive in the region where the current gain of the transistor decreases with frequency (from fT/hfeto fT) the input impedance looking into the base ends up looking like a negative resistance in this region.

author: dr.diesel
author_rank: Super Contributor
timestamp: January 05, 2014, 09:27:34 pm
content: Quote from: c4757p on January 05, 2014, 08:06:58 pmThis is actually something I've been meaning to hit Dave with, just haven't gathered my thoughts. Supplying kits out of your dorm room would be a PITA, sorting bags of parts, enclosures etc, not to mention the time required. You'd have to begin just providing the documentation and selling the PCBs, with BOMs from Digikey or something, all support via a forum. Start with something less complicated than the FG, either the PS or the eLoad, something that can build capital, even if only a little.Even though I've been doing this for 20 years, I still buy anything I can as a kit. I buy tons of kits, I give them away as X-Mas present to all kinds of people. I'd personally buy several of any kit you're willing to sell.Find something to start with, run it through here like you've been doing, maybe a group buy? Good web docs, YT video, get Dave to review and link to it?I Donno, just thinking out loud.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 09:29:14 pm
content: Quote from: megajocke on January 05, 2014, 09:25:35 pmThe current sense resistor will help as well. Though I will keep it. As I said, it is harmless, and at least might be useful.

author: liquibyte
author_rank: Frequent Contributor
timestamp: January 05, 2014, 09:36:22 pm
content: Quote from: dr.diesel on January 05, 2014, 09:27:34 pm+1this. I'd buy a board with a BOM for the parts and put stuff together that I have and get what I don't.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 09:51:28 pm
content: That's what I originally wanted to do but I wasn't sure if anyone would buy it, if they had to go off to Mouser or DigiKey or wherever and get parts. So, am I wrong? Could it be successful in the beginning as a BOM+PCB+manual kit?

author: liquibyte
author_rank: Frequent Contributor
timestamp: January 05, 2014, 10:02:55 pm
content: Put it together and let me know how much and I'll get one. I have an 18V toroid I'd like to use. Do you still plan on the 20V kit?

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 10:03:52 pm
content: Yep, it's just a change of a couple resistor values and DZ1.Once I have it fully tested, I am going to start by ordering a first batch of 20 PCBs. I ordered ten panel meters to modify with a custom scale, and I'll include those with the first ten. I will try to keep including them, as I don't want modifying things to be part of the build (well, Iwasplanning on having a winding added to the transformer!), but I don't imagine shipping will be very fast, so if you buy a kit after the first ten and I haven't received another shipment of meters, you're going to have to source and mod your own. I will also include a printout of the manual (including the schematic, which is oversized - U.S. ledger/tabloid, 280x430mm - and rather hard to read if you shrink it and then print).

author: blackdog
author_rank: Frequent Contributor
timestamp: January 05, 2014, 10:08:28 pm
content: Hi c4757p,Can you explane how your Voltage Reference is working...Q4a base and collector are shorted togetter?Schematic error or is Blackdog is a ...OK, the 100 a 150 Ohm base resistor is always necesary, but you already now that :-)Lets look at R23 and what is connected on the left site C5 33pf and several transistors, at least 50pf, this wil give about 25Khz -3dB.Is you power supply fast enough for transient loads?I dit a lot of testing on my design of a LAB powersupply, take a look if you want on this website, use google translate becaus its in Dutch, sorry...http://www.circuitsonline.net/forum/view/110029/8Kind regarts,Blackdog

author: dr.diesel
author_rank: Super Contributor
timestamp: January 05, 2014, 10:12:36 pm
content: Quote from: c4757p on January 05, 2014, 09:51:28 pmIf you make it easy, I'd say yes. When doing the BOM make sure and include vendor part numbers for each part.

author: c4757p
author_rank: Super Contributor
timestamp: January 05, 2014, 10:29:32 pm
content: Q4A base and collector are shorted in net name only. The base runs directly to the top of the "compound diode", buffering the voltage exactly at that point (the reference and feedback are treated as a differential pair at all times). The collector is indeed at the same voltage, but an emitter follower will work just fine with the base and collector at the same potential. You just can't forward-bias the B-C diode.Your -3db point is off - keep in mind that point sees a Thevenin impedance of 18k, not 120k. It should be closer to 170kHz. It's not extremely fast - in SPICE the transient response time is about 200us for a rising load and 1ms for a falling load; I'm not going to bother testing my prototype for that because that's going to be layout-dependent. I don't think anybody is going to be too upset that it's not fast, though. In SPICE only, again (real data will come when I have one properly assembled), the output voltage spikes by no more than 30mV with a 500us rise time on the load and 0.5V with a 1us rise time. I'd expect test lead inductance to contribute worse than that...I'll read your website when my eyes aren't tired; Google Translate butchers it!Quote from: dr.diesel on January 05, 2014, 10:12:36 pmI'll make them directly compatible with Mouser and DigiKey's BOM import tool.

author: megajocke
author_rank: Regular Contributor
timestamp: January 06, 2014, 12:03:13 am
content: But the error amplifier is an integrator -- the -3 dB point will hopefully be at a very low frequency.With the FB- node as input and the collector of Q7 as the output, the error amplifier behaves as an inverting integrator with a gain-bandwidth product of 40 kHz (the impedance of R23 and C5 have the same magnitude at this frequency).The gain from the FB+ input will be the same integrator (but noninverting) at low frequency up to 40 kHz, above which the gain goes to 1 until some high frequency where the error amplifier itself starts to run out of gain.So you would end up with a loop crossover frequency of about 40 kHz if it weren't for the output capacitor (and its ESR) which forms a divider together with the current sensing resistor and output impedance of the output amplifier.It can be insightful to look at the output impedance. It should end up looking like about 5 µH in parallell with a 1 ohm resistor and the output capacitor. There would also be some resistance in series with the fictional inductor because of the finite low frequency gain of the error amplifier.The attached simulation shows what would happen in voltage mode with the error amplifier approximated as close to ideal. The plot shows output impedance and the impedance of the equivalent to the right in ohms. The output impedance looks well-damped enough.Modifying the compensation capacitor value changes the equivalent output inductance in proportion. (edit: oops, did a brainfart there... had written inverse proportion by mistake)

author: c4757p
author_rank: Super Contributor
timestamp: January 06, 2014, 01:22:38 am
content: Yeah, you are right.I like that way of analyzing the circuit. I've seen plenty of more "proper" ways to test the response, but somehow I missed that. Thank you! I'll play around with it a bit.In the real circuit, 33pF wasn't bad, but did have a bit of peaking. 470pF + (33pF || 4.7Meg) smoothed it out completely. I don't think I'll have to do that, but I will keep it in mind.

author: flano
author_rank: Contributor
timestamp: January 06, 2014, 10:27:56 am
content: Chris,Any thoughts of putting a current limit LED?Love your work on both the Function Gen and this project.PCB, BOM and Doco would be fine.Thanks Mike

author: c4757p
author_rank: Super Contributor
timestamp: January 06, 2014, 12:52:52 pm
content: A current limit LED would be very easy. Not a bad idea

author: c4757p
author_rank: Super Contributor
timestamp: January 06, 2014, 04:09:49 pm
content: I had to move up to the 100x100mm PCB size bracket, and for the sake of spreading things out a bit more to make a neater PCB, I went all the way to 100x100. Here's the revision B PCB.

author: Thor-Arne
author_rank: Unknown
timestamp: January 06, 2014, 07:30:37 pm
content: Sorry about the late reply on this, busy with kids and life in general.I haven't ordered much semiconductors from AliExpress, but quite a few project boxes and such.For inexpensive parts like the ones above I don't think the risk is that big, especially if the seller has good feedback score.If you order parts from Ali, I recommend that you compare prices for with/without free shipping. For some of the tings I've ordered the free shipping ones actually became more expensive.I've only ordered some diodes and leds from AliExpress, nothing wrong with those at least.Anyway,MMBT3904x100 USD2.42MMBT3906x100 USD1.81MMBT4148x200 USD15.00Seems like the MMBT4148 was expensive. perhapsthiscan be used instead?Also, searcing for "3904 sot-23" and "3906 sot-23" both yield better prices than for the MMBT* types.Tip, if you need bigger quantities than the seller lists, always ask for a quote.

author: mrkev
author_rank: Regular Contributor
timestamp: January 08, 2014, 09:24:18 pm
content: Quote from: blackdog on January 05, 2014, 10:08:28 pmWell, Blackdog is a ...thenJust kidding... You probably missed that Q4a is effectively just a diode and it can be, as the active load Q16a and Q16b is two P-N passes higher than V+, and that differential pair (Q5A and Q5B) can (therefore) go quite high...Also, because Q4 is a diode, any base resistor is pointless..

author: megajocke
author_rank: Regular Contributor
timestamp: January 08, 2014, 10:56:12 pm
content: I don't know if I'd trust a 4148 to survive charging the smoothing cap in the D11 position. And with that diode in place is there really a need for the diode in series with the voltage error amplifier? Using a midpoint of the diode string won't help much in any case though. It's a circle of four diodes so it would conduct in both directions anyways.

author: c4757p
author_rank: Super Contributor
timestamp: January 08, 2014, 11:07:39 pm
content: You're right, IFSMis only 4A. I thought it was higher. I'll change that to another 4001.Shame on me for thinking I was more familiar with a common part.Quote from: megajocke on January 08, 2014, 10:56:12 pmYou know, I don't remember why I did that anymore. I do remember that it stopped a large flow of current in the simulation under some unlikely output conditions... but I can't remember what those conditions were, and I can't make it happen again.

author: c4757p
author_rank: Super Contributor
timestamp: January 09, 2014, 04:57:35 pm
content: The text has moved along a bit further - some corrections, some updates to the circuits, and the ToO is written through the voltage error amplifier. I'll post again when I have the full ToO complete.I've also updated the PCB. Not much has changed, but I labeled things a bit better. I also moved the output and sense jacks to put pairs together.

author: c4757p
author_rank: Super Contributor
timestamp: January 15, 2014, 06:46:10 pm
content: This image is brought to you by the letter I, for "goddamnpost from China is slow" - er, I mean "impatience".(And yeah, that's a shitty specimen, but itis"good enough")

author: c4757p
author_rank: Super Contributor
timestamp: January 16, 2014, 05:44:29 pm
content: Quick meter prototype. A few things need to be adjusted (arc radius is obviously wrong, for instance, and text positions need to be tweaked), but I was more concerned with it looking at least semi-professional, and I think it does.These little $1.20 meters are actually pretty good. They are small, which I didn't realize, but I like the size. Very linear, and even though the null screw is under the cover, they seem to hold their null well. The resistor inside them looks to have been soldered by a three-year-old (it probablywas), but those are coming out anyway. Fairly high current (900uA full scale); that could be good or bad. Acceptable here.(Initial accuracy was ghastly. 10% out. I suspect they're supposed to be 1mA full scale, not 900uA, but that's what I measured.)The low voltage version will allow higher current (equal power), so that will have a different meter face. Meter faces will be printed on white card and sprayed with UV-resistant fixative.

author: rdl
author_rank: Super Contributor
timestamp: January 16, 2014, 06:29:38 pm
content: Okay, I'm not trying to be a jerk or anything because it looks pretty good, but think about that "100 milliamps". What does the meter actually display? This actually something car manufacturers do all the time and it has always bugged me.The tach in my truck reads from 0 to 6, but the label says "RPM x 1000". Does this mean the engine only goes from 0 to .06 RPM?I had a Chevelle in the old days, and a Mitsubishi more recently, where the tach had numbers from 0 to 70 and was labeled "RPM / 100", which actually makes sense. I don't know, I guess it's just a pet peeve of mine.

author: c4757p
author_rank: Super Contributor
timestamp: January 16, 2014, 06:53:02 pm
content: I think it is correct. The unit is "100 mA". When it's pointing at 2, that is two units of 100 mA, or 200mA., in the same way that when it points at 20 on the top scale, it is indicating twenty units of 1V.I could understand confusion (or.... fake confusion) if I used a multiplication or division sign, but I did not.Edit: Just finished a test and resistorectomy on all ten, andholy crapthese have a bell curve to rival Big Ben. 2.5% my ass! That's OK, they were getting trimmers anyway.

author: Thor-Arne
author_rank: Unknown
timestamp: January 16, 2014, 07:52:53 pm
content: Quote from: c4757p on January 16, 2014, 05:44:29 pmLooking good.Perhaps a little to wide lines on the scale if I have to comment on something.

author: c4757p
author_rank: Super Contributor
timestamp: January 16, 2014, 07:54:29 pm
content: I agree, I made them a bit thinner. I still like them thicker than the usual, though - easy to read at a distance.

author: codeboy2k
author_rank: Super Contributor
timestamp: January 17, 2014, 09:16:05 am
content: Quote from: c4757p on January 16, 2014, 06:53:02 pmMeter looks great! yes, one you fix the arc angle it will be even better !Regarding the comments about 100 milliamp on the bottom scale.. I have a suggestion.. you could but 1, 2, 3, 4, 500mA , i.e. just label the last one as 500mA and the rest are single digits. Or put 1,2,3,4,500 and just put the text at the bottom middle of the meter as "MILLIAMPS" not "100 MILLIAMPS"Although I do agree with your thinking re: not putting the divide or multiply sign.. that just confuses one way or the other.Was that PC board you made etched or routed? Looks almost like it could be routed but the right edge in the picture looks like it was etched, so I was not sure.I like your silk screen with the sections grouped and labeled ! good work!

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2014, 11:50:48 am
content: Thanks for the kind words.I considered labeling the meter like that, but I decided that the overly literal perfectionist side of me wouldhatethat... And it's too late now, I just made a big batch of 3 x 18 meter faces, all printed, coated and cut out.The PCB was etched. I stopped the etch early for the sake of the couple finely spaced traces (I didnotdesign this board for home etching...... it didn't work very well) and then touched it up manually with a knife, so that might be why it looks a bit odd.Both PCB and schematic are still being changed a bit. I'm making a few subtle changes as I build and exercise the circuits (and perhaps one not-so-subtle change - the line regulation isn't quite what I hoped, might have to change the local regulator to fix that). Also, I put the trimmers for the meter on-board, switched to a bigger TVS diode (one that can absolutely, without a doubt handle the full impulse of popping the fuse under some fairly heavy overload conditions), and added more of the off-board wiring to the schematic.Speaking of off-board wiring - it occurs to me that not a lot of people know this trick, so I thought I'd share: In KiCad, if you want to place a component that does not exist in the PCB (for off-board wiring diagrams, symbols, etc.), just add a # symbol at the beginning of its reference designator. It will then be omitted from the netlist and PCB. Then, if you like, you can give it a "different", non-# refdes by marking the real one invisible and using one of the custom attributes.

author: Thor-Arne
author_rank: Unknown
timestamp: January 17, 2014, 01:50:19 pm
content: I'm looking forward to the next update on this project, really promising.Have you designed the pcb to a specific enclosure?Quote from: c4757p on January 17, 2014, 11:50:48 amGreat tip, thanks.

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2014, 02:15:54 pm
content: Quote from: Thor-Arne on January 17, 2014, 01:50:19 pmI have not. Nice, chunky metal enclosures are often rather expensive, but it's usually pretty easy to find something suitable cheap if you don't need a certain, exact style. If I had built this around one enclosure the cost would have gone up quite a bit.Quote from: Thor-Arne on January 17, 2014, 01:50:19 pmYou're welcome! This is how it internally excludes power symbols from the netlist, so it's nottoohackish - I don't expect it to break with an update or anything.

author: Thor-Arne
author_rank: Unknown
timestamp: January 17, 2014, 04:24:20 pm
content: I tend to source my enclosures from AliExpress, especially the plastic ones. I have good experiences withthisstore.I guess you have been reading through the KiCad source to find useful tings like this?

author: Jebnor
author_rank: Regular Contributor
timestamp: January 17, 2014, 04:42:36 pm
content: A couple noted regarding the manual uploaded 09 January 2014. (If you're still accepting constructive criticism that is.S1.2 Par.5: "Both the nominal 650mV threshold voltage and the300330(ohm)..."S1.2 Par.5: ~middle ~middle "A typical A typical"S1.2 Following the Error calculations: The paragraph begins "This 2mA is drawn..." It's a little odd as the calculation was finished with 130uA, then you jump back a calculation and talk about 2mA. Might I suggest moving the reasoning and details of the 2mA for ZD1 to a paragraph before the error calculations. Something like: "The VEE regulator is more complicated" -> Paragraph about ZD1 and mA requirements and stability -> Current source Paragraph -> Error Calcs -> Paragraph on error effects.S1.2 Final Par: Change "It" to "Q3" in Sentence 2. "It" is ambiguous.S1.3 P1: "input power rejection compounds" comes in from no where. I think it needs some explanation.S1.3 Table: Needs a title/label.General: pick a consistent scheme for your diagrams. Fig1.1 used blue and Red with dotted and dashed lines, where Fig1.4 uses red and Green with all dashed lines. Add a legend to Fig 1.4, which will then eliminate the need for theitalicsnote while referencing Fig1.4 (any such notes, if required, should be with the figure.) In my experience, green is a difficult colour to get right in documents, getting a green dark enough such that it prints well in B+W makes it hard to distinguish from blue. I stick with Red/Blue. Further, dotted lines (such as those in Fig1.1) are more difficult to follow with the eye and don't scale well when printed, dashed (------) and dash-dot (-.-.-.-.-.-) lines are best IMNSHO.Nits/style:Fig1.1: 1) The {Rectifier -> Regulator -> OUT} Main power path is difficult to follow, too many 90s in the line. Possibly make the Regulator more "inline" from Rectifier to out. i.e. left to right. 2) The Power line isn't easily distinguished from the 'low power' lines such as those driving the current sources off Vcc.Table 1: Spacing... (As I'm sure you already know.)One final thing.LaTeX FTW!PS: I'm learning a lot from this. Keep up the good work.

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2014, 04:54:32 pm
content: I'm still accepting criticism, but some is going to be outdated, because I've done a lot of work on the manual that hasn't been posted yet.However, you seem to have noticed mostly things I haven't.300 -> 330 ohm: got itA typical A typical -> got it2mA/130uA -> Good point, thank you!it -> Q3 -> Another good point.compounds -> And another.Table title -> And another.Diagrams: Yes, the colors need to be standardized. I used red/blue in the first diagram for +ve/-ve, but then as I started using blue for annotations, I dropped that. I'll fix this. And you're right about the dotted lines.Block diagram power path: Yes, the main power path should be better marked.Table spacing: Noted.Quote from: Jebnor on January 17, 2014, 04:42:36 pmFTW indeedAnd XCircuit for diagramsTBH I've used LaTeX almost exclusively for long enough that I don't even know how I'd manage a somewhat large document in a traditional word processor. ToC, standardization of styles, figure positions, etc... And I'm significantly less productive on a keyboard without vim editing commands.

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2014, 06:32:20 pm
content: Transient response. First 25V then 10V at a 500mA switched load. The voltage never spikes by more than 35mV or dips by more than 50mV, response in 25us.Load regulation is within 65ppm from 0-500mA.Voltage stability is good enough that with no cover, I can watch the setpoint drift (by about 500uV on 10V) as I move and the air around me blows.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 17, 2014, 11:23:37 pm
content: On a practical note, what happens if the sense feedback becomes disconnected?

author: c4757p
author_rank: Super Contributor
timestamp: January 17, 2014, 11:45:07 pm
content: There is a pulldown resistor on the sense input, so the output will drop. It may not drop all the way to zero, but at least to 3V or so.Also, I recommend installing 10-100 ohm resistors linking sense to output on the back of the binding posts to provide an even better default. Actual cables will have a lower impedance and "override" the resistors.

author: sync
author_rank: Frequent Contributor
timestamp: January 17, 2014, 11:54:51 pm
content: With a pull down resistor on + sense the output should rise.Don't forget a diode to protect the 10-100ohm resistor from over current, e.g. connecting + sense to negative terminal. Then the output rise and the output voltage is across the resistor.

author: Andy Watson
author_rank: Super Contributor
timestamp: January 18, 2014, 12:06:13 am
content: Quote from: c4757p on January 17, 2014, 11:45:07 pmWill it ?R24? Spotted that, but, what happens if the demand is more than half? I think the output will go to full bananas!

author: c4757p
author_rank: Super Contributor
timestamp: January 18, 2014, 01:31:04 am
content: D'oh.Clearly I screwed up that section. Looking more closely, I don't know why I ever thought it would work.I'm going to take those resistors (and diodes) that I was going to have placed on the sense jacks, and just put them on the PCB. Then there are no bananas.I was just about to test that, too...

author: c4757p
author_rank: Super Contributor
timestamp: January 20, 2014, 03:44:30 am
content: Hmm.... the local regulator definitely needs some form of current limit... the magic smoke comes outveryquickly if shorted

author: codeboy2k
author_rank: Super Contributor
timestamp: January 20, 2014, 03:42:17 pm
content: Quote from: c4757p on January 20, 2014, 03:44:30 amCan we custom order the smoke color

author: c4757p
author_rank: Super Contributor
timestamp: January 20, 2014, 03:44:20 pm
content: Any customer can have magic smoke in any color that he wants so long as it is blue.

author: idpromnut
author_rank: Unknown
timestamp: January 21, 2014, 01:35:47 pm
content: Is there a board available that you could shot me? I'd be interested in testing it out

author: c4757p
author_rank: Super Contributor
timestamp: January 21, 2014, 02:12:13 pm
content: Not yet. Still working on my home-etched one.

author: c4757p
author_rank: Super Contributor
timestamp: January 24, 2014, 08:51:52 pm
content: Updated schematic. I'm etching another PCB today or tomorrow, but I have to order parts, because.....- Local regulator has been updated. It is now short-circuit safe. May all the transistors that died when I found out how horriblynotshort-circuit safe it was rest in piece(s).- It now also doubles as the voltage reference, rather than having two separate parts.I've got it on GitHub and will post the URL when I get the source files cleaned up a bit.

author: c4757p
author_rank: Super Contributor
timestamp: January 25, 2014, 04:23:04 am
content: Possibly final schematic and PCB.

author: c4757p
author_rank: Super Contributor
timestamp: January 31, 2014, 09:47:27 pm
content: Sorry for the long delay, but... other things to do.I held off on ordering parts because I was finishing another circuit design too and wanted to order them together. Will order tonight...

author: Thor-Arne
author_rank: Unknown
timestamp: March 30, 2014, 04:37:25 pm
content: What's the status of this project?

author: c4757p
author_rank: Super Contributor
timestamp: March 30, 2014, 04:49:44 pm
content: Slow. Sorry - I've been busy. Delay after delay after delay...I've made quite a few changes after some testing. I've madewaytoo many "OK, this is the final version, PCBs soon!" promises though, so I'm not going to post and boast until I have it thoroughly tested

author: Thor-Arne
author_rank: Unknown
timestamp: March 30, 2014, 04:55:34 pm
content: That's ok. Just wondering since it's been a while.

author: c4757p
author_rank: Super Contributor
timestamp: April 20, 2014, 07:08:04 pm
content: Quote from: Thor-Arne on March 30, 2014, 04:55:34 pmYou're not kidding - here I am, back in almost a month, and it'sstillnot done!Here's a new schematic. Hmm... let me see if I can summarize the changes. It's been a while.Most obvious - schematic has been broken into a hierarchical with block diagram. This makes documentation easier, and it can be printed onto standard US Letter paper. I'll check that it also fits on A4.Some areas have functional explanations on the schematic itself. These are not meant to replace the ones in the manual.A stiffer current source biasing the error amplifier means better CMRR - better load regulation.Current sense is now ground-referenced, making that section no longer shitty.Thermal cutoff behaves better: pseudo-thyristor latch current no longer flows on the feedback path.Local rail is now -12V on all versions of the circuit, rather than -32V on the high voltage one and -20V on the low voltage one.

author: Thor-Arne
author_rank: Unknown
timestamp: April 21, 2014, 08:21:01 am
content: Great!Nice to see progress on this project.

author: at2marty
author_rank: Regular Contributor
timestamp: April 21, 2014, 07:47:17 pm
content: Very nice project! I thought you mentioned earlier in this thread about putting stuff on Github. Can you provide a link?

author: c4757p
author_rank: Super Contributor
timestamp: May 05, 2014, 12:37:45 am
content: A few changes again...Decided I hate the multiple-page schematic. It's just too much for something like this - obscures details until you flip the page.Completely new PCB.Quote from: at2marty on April 21, 2014, 07:47:17 pmYup,right here. Though, pretty much everything outside Proj-Main/ is out of date right now.

author: c4757p
author_rank: Super Contributor
timestamp: May 16, 2014, 02:32:39 am
content: Final version which was sent out this morning:

author: cellularmitosis
author_rank: Unknown
timestamp: May 16, 2014, 06:12:23 am
content: Woo hoo!

author: kizzap
author_rank: Unknown
timestamp: May 16, 2014, 07:57:52 am
content: Quick: everyone point out all the errors!

author: jaxbird
author_rank: Frequent Contributor
timestamp: May 16, 2014, 02:23:49 pm
content: Looks niceAny specific reason for not including component labels (R1, R2 etc) in the silk screen?

author: c4757p
author_rank: Super Contributor
timestamp: May 16, 2014, 02:40:17 pm
content: In some places, it was surprisingly difficult to make them fit (while still being obvious which label went to which part). I'd rather leave them off than have them be confusing. The assembly directions will have expanded diagrams of each section with the parts visibly labeled.

author: jaxbird
author_rank: Frequent Contributor
timestamp: May 16, 2014, 03:02:13 pm
content: Quote from: c4757p on May 16, 2014, 02:40:17 pmYeah, it can be a mess sometimes.. Not so important as long as you have a nice big drawing with the labels.It does look very nice and clean, I like the groupings.

author: c4757p
author_rank: Super Contributor
timestamp: June 14, 2014, 01:26:22 am
content: Got the PCBs, and did a bit of testing today; more tomorrow. Here's the line regulation of the local regulator block:

author: c4757p
author_rank: Super Contributor
timestamp: June 14, 2014, 05:22:21 pm
content: More local regulator testing - power supply rejection/ripple rejection vs. frequency. LM317 is included in the plot for comparison. The performance isn't amazing at higher frequencies, but it doesn't need to be, and it's still quite good at the frequency of the line ripple.

author: Thor-Arne
author_rank: Unknown
timestamp: June 14, 2014, 09:49:13 pm
content: Nice.Will the measurement setup be included in the doc eventually?That would be very useful to me for one as I have no clue.

author: c4757p
author_rank: Super Contributor
timestamp: June 14, 2014, 10:17:47 pm
content: Yes, it will be, though I can show what I did briefly here, in pictures at least.Line regulation: Truly clean measurements, for a smooth plot, were difficult to pull out of the random noise of thermal changes in the environment. Shielding from air movement helped, but I still had to average over a long enough time that I wanted to prevent ambient temperature change from causing error. The board was placed into a controlled chamber (actually a PID+toaster reflow oven packed with ceramic tiles) and stabilized at 60°C. A very stable power supply (Power Designs 2005) was used to offset the -12V output to allow more measurement precision, and I used my Fluke 45 to output data to my PC, where it was low pass filtered to get clean measurements. I stepped over a range of input voltages, then recorded the output delta after the LPF settled.Load regulation: The main reservoir capacitor was removed to allow AC on the input side. I put my main power supply in series with a function generator, to inject ripple at various frequencies. I kept the input amplitude to 1Vp-p, and measured both the input-side and output-side ripple on an oscilloscope to calculate the rejection. Sensitive, differential amplifiers were necessary, at least at low frequencies where the rejection was very high.I kept the board in the "thermal chamber", now fully cooled back to ambient, for this test, as the metal case would shield against interference.Note that the ripple rejection is actuallybetterunder 100 Hz than theDC line regulation. This is possible because a large component of the line regulation error is due to self heating, and so has a long (> 1 minute) time constant.

author: Thor-Arne
author_rank: Unknown
timestamp: June 15, 2014, 09:01:07 am
content: Nice, thanks.

author: szabolcsx
author_rank: Contributor
timestamp: June 26, 2014, 07:50:39 pm
content: Hi, I really appreciate your effort to design a power supply using only discrete components. I'm a beginner and there are some "dark spots" for me in schematics. May I ask when the documentation will be finished? The concrete part of schematics which isn't clear for me is the current sense amplifier. I tried to simulate using LTSpice but with no luck. I don't understand why it's connected to +2V.

author: c4757p
author_rank: Super Contributor
timestamp: June 26, 2014, 09:33:53 pm
content: Hi, szabolcsx. Yeah, as you can probably see from this thread, electronics has been moving slowly for me lately.The documentation's a ways off as is just about everything else.Okay, the current sense amplifier. First, the simple part: why is it connected to +2V? Because it needs "headroom" above the 0V positive output line. In order for it to work, Q23A has to pull its collector at least 1.3V (two transistor thresholds) down, so that both Q24 and Q19 turn on. If it were connected to 0V instead, the collector would drop below the base, forward-biasing the base-collector junction and preventing the transistor from turning on any more.Now, for the actual operation: R47 is in the path of the output current, and acts as a sense resistor. The left side of that resistor sits at 0V, and the right side drops down by Ohm's law as the current through it increases.A voltage divider between 0V (the left side of R47) and -12V allows you to set a threshold voltage, which isconnected to Q23A's base. The actual current sense voltage goes to Q23B's base. The emitters, which are joined together, will go to whichever voltage is lower, and then R44 acts as a current source to pass about 1mA through the two transistors.Normally, the current sense voltage (on Q23B) will be higher. Q23B is then the only transistor whose base is above the base-emitter threshold, so only Q23B is active. When the current sense voltage falls to the threshold voltage, though, both transistors have equal base voltages, and theybothturn on. If it falls even more, only Q23A will remain on.If the balance shifts enough towards Q23A that there is about 650µA flowing through it, each of R42 and R43 will produce 0.65V, about a transistor threshold, turning on both Q24 and Q19. Q19 sources current to LED DS2, activating the 'limit' LED. Q24 pushes the FB+ line higher, which makes the main error amplifier think the output is too large. The output is then decreased until Q23A and Q23B are balanced.Let me know if I haven't explained something well, as I don't know what point you're at in your learning.Would you care to share your LTspice file with me?

author: Kevin.D
author_rank: Frequent Contributor
timestamp: June 28, 2014, 09:58:10 am
content: Hi there . Where are your latest LTspice simulation files ,the ones posted back on page 2 of this thread dont match with your later schematics .Thanx

author: c4757p
author_rank: Super Contributor
timestamp: June 28, 2014, 10:25:03 am
content: Try the ones in Github a few posts up. But I haven't really been using SPICE extensively for this project, so I'm not sure how current they are.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: June 28, 2014, 04:10:40 pm
content: Latest git hub (may) ones Doesn't work , some .libs and symbols missing.

author: szabolcsx
author_rank: Contributor
timestamp: July 05, 2014, 07:17:28 pm
content: Sorry for the late reply, I had exams. Here is the LTSpice file. I wanted to measure the current on high side.

author: c4757p
author_rank: Super Contributor
timestamp: July 05, 2014, 07:53:37 pm
content: I thought you were trying to simulate the amplifier in this kit! I'm sorry, I've got too much going on right now to walk you through designing a different one. Perhaps you could try posting a new thread?

author: c4757p
author_rank: Super Contributor
timestamp: July 30, 2014, 09:45:12 pm
content: Everyone - I know this project has been neglected - I came off a hell of a semester into a hell of a summer, and will probably have another hell of a year to follow it.I am not abandoning this project, but as so many other things have been demanding my attention lately, I cannot promise anything. Frankly, it's been so long and I've had so much on my mind lately as to pretty much lose interest - though I still like this project and will still complete it eventually. Don't be surprised if it takes another year....... That's what happens when you start a complicated project and assume the rest of your life won't get in the way.I've got another couple of things slowly coming along as well, which I'll postlaterin development rather than posting a long string of "I promise you guys, it's almost done again!". Wouldn't be surprised if school and life took precedence again.

author: Jebnor
author_rank: Regular Contributor
timestamp: August 12, 2014, 02:05:27 am
content: c4757p, Thanks for all your good work. I have learnt a lot reading this thread. No need to apologize for life, we understand.When you have the time and inclination to get back at this project, I'd like to see it completed. No rush.