finished building lab power supply (CO voeding 2019) - Page 1
Forum section: electronics / projects

author: exe
author_rank: Unknown
timestamp: July 15, 2019, 08:11:57 pm
content: My friends,I just finished a four-month project. It's a lab power supply. It was quite a challenge to do the assembly. As a teaser, posting here a photo. I want to make a video on it, so people won't do same mistake as I did.Spoiler alert: I screwed it, but it was fun.

author: xavier60
author_rank: Super Contributor
timestamp: August 05, 2019, 01:52:14 am
content: Looks very nice from here.Has the load transient response been tested? The gain of the CV op-amp is set unusually high.

author: ledtester
author_rank: Super Contributor
timestamp: August 05, 2019, 02:05:22 am
content: Quote from: exe on July 15, 2019, 08:11:57 pmThat would be very nice - please post it!Quote from: xavier60 on August 05, 2019, 01:52:14 amHow can you tell that from just those pictures???

author: xavier60
author_rank: Super Contributor
timestamp: August 05, 2019, 02:11:29 am
content: This is the page with a link to the schematic, I think.https://www.circuitsonline.net/forum/view/144222https://www.circuitsonline.net/forum/view/144126

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 03:25:34 am
content: you should make it so if that thing malfunctions the heat sink is prevented from melting through the plastic, at least add some bent wire supports under it to keep it elevated if it gets roaring.It has a thermostat right? and yes commercial supplies have thermostats on the heat sinks (i.e. lambda)

author: exe
author_rank: Unknown
timestamp: August 05, 2019, 12:43:38 pm
content: Quote from: coppercone2 on August 05, 2019, 03:25:34 amUnfortunately, it doesn't. But I adjusted maximum current so under no condition it overheats. I also added fuses with tight ratings on primary and secondary sides. Still, plastic is only good up to 70C or so. Next time I'll try to use nylon, it should be more heat-resistant.Current biggest bottleneck is bridge rectifier, those I had are quite warm at currents above 1A. So I limited current output to 0.9A. The next issue is thermal transfer through insulation pad is quite poor. So, the current is also limited to the value where transistors are below 70C, while heatsink is about 60 in the hottest spot. It was tested with ambient temperature of ~20C, but it should be good at 30+C as well.In practice it's not that warm, as I rarely need full current at zero volts. But performance is still disappointing, I was hoping to get 2A out of it.Thank you for your support, I'll shoot a video where I show all the intimate details of it

author: coppercone2
author_rank: Super Contributor
timestamp: August 05, 2019, 10:56:19 pm
content: keep in mind voltage current power relationship and voltage instability of mains (so ability of fuse to limit power is based on voltage)you designed mains nominal (probobly), does it work under other conditions?

author: exe
author_rank: Unknown
timestamp: August 06, 2019, 07:32:11 am
content: Quote from: coppercone2 on August 05, 2019, 10:56:19 pmI'm not sure I understand. Fuses are not to limit power, they are to prevent catastrophic failure. Fuses trip on current, not on voltage (unless there is not enough voltage to develop enough current to trip fuses). Fuses are install on transformer's windings, on all of them because I'm paranoid.Quote from: coppercone2 on August 05, 2019, 10:56:19 pmIn my designs I try to accommodate the lowest mains voltage, and transformer regulation, and on top of that add a bit of margin. This is not my design, but I verified performance under my current mains voltage (~239V), and I add some margin so that it should work down to approximately 220V at full load. The margins required for1) auxiliary power supply that supplies error amplifier and front panel (+12V and -12V)2) for tap switching, the PSU has two output ranges, 0-8.2V, and 8.2V+, switching done with some hysteresis to prevent oscillation.I don't have a variac to test under worst condition, so I used some math, taking into account transformer regulation specified in the datasheet.

author: markce
author_rank: Regular Contributor
timestamp: August 06, 2019, 01:43:15 pm
content: Some questions and remarks:- The bridge rectifier needs cooling as indicated in the building instructions from CO.- You did use only one TO220 regulator transistor? What kind of insulator did you mount this on?- What are the specs or dimensions of your transformer?

author: exe
author_rank: Unknown
timestamp: August 06, 2019, 07:47:41 pm
content: Quote from: markce on August 06, 2019, 01:43:15 pmI forgot to mention one thing: I used parts parts laying in mytrash binlab. Like, I didn't buy tranny, I salvaged it from one makers lab back in 2014. The heatsink was meant for another project, it was bough for a sound amplifier, which I couldn't finish. The funny thing, after finishing this power supply, I also finished soldering amplifier, but now I don't have one heatsink to finish assembly. So... I'm bad at planning. (the amplifier, btw, is famous P101 from almighty Rod Elliott based on lateral mosfetsproduced by nude virgins). Now, given the effort I put into designing enclosure, etc, I'd probably make different decisions. But back in Febrary when I bought it, it looked like an easy project.1) Ah, instructions, right. I don't speak Dutch yet, so, mostly looked at schematics. That was an oversight from me, quite disappointing. For some reason I expected a much better performance. If I find a schottky equivalent in GBU package I'll replace it. Just I didn't have any at hand and I regret I didn't buy one.2) I used both transistors to have more even heat spread, insulation was the one supplied with the kit3) It's 30VA 2x9V tranny, diameter 70mm, height 30, partnumber RS0030P1-2-009. I adjusted resistors etc on pcbs accordingly. Yeah, secondary voltage is even lower than ~12 required for aux power.

author: markce
author_rank: Regular Contributor
timestamp: August 07, 2019, 11:19:06 am
content: You can easily get better performance if upgrade your build.1) The Dutch language need not be a problem. Have you asked the guys at CO for some pointers with your build? There is also a google-translate...The design of the CO lab supply is aimed at reducing power dissipation, at cost of some efficiency. It uses a silicon bridge rectifier, switching diode/FET and darlington regulator transitors. This conficguration has quite some voltage drop and is not suitable for a low voltage lab supply. The design is for 25V/3A or 30V/2.5A output.2) SIL-pad insulators need quite some pressure for good contact. The darlington transistors in the kit are 'starters'. There was some discussion on CO forum about the choice. You could upgrade them to TIP142's for better heath transfer and wider SOAR.3) Main problem with your build: The 30VA 2x9V tranny is way too small. Use a 120VA 2x15V transformer.4) Second: A closed plastic (PLA) enclosure is not a good idea for a lab supply.Get a well vented metal enclosure.

author: blackdog
author_rank: Frequent Contributor
timestamp: August 07, 2019, 06:40:59 pm
content: Hi xavier60The gain of the voltage loop IC is the reference voltage multiplied by the maximum desired output voltage.The gain (maximum output voltage) is set by the resistors R30 and R54 and is 6.8 times.The 5V reference is built on with U3 a TL431 and Q14 and is +5V.If there's any more explanation needed, I'd love to hear it.Kind regards,Bram

author: xavier60
author_rank: Super Contributor
timestamp: August 07, 2019, 08:46:37 pm
content: I'm mainly curious about the high frequency gain of the CV op-amp set by the compensation components C30, R59, R31.It is about 34 at above 50Khz.The design would have a very fast load transient response but is it stable?I have some OPA2192 op-amps that I could experiment with.

author: exe
author_rank: Unknown
timestamp: August 07, 2019, 08:48:33 pm
content: Quote from: markce on August 07, 2019, 11:19:06 amThank you very much for your suggestions. Let me answer to some of your concerns.1. Tranny. I think it is fine, it can deliver what I need. I don't need high voltage. And I got it for free. For bridge rectifier I have an idea:https://www.diyaudio.com/forums/group-buys/333844-ideal-bridge-rectifier-gb.html.2. Enclosure is PETG, PLA didn't work well in my heating tests. PETG is not the best choice either, but that is what I got at hand. The enclosure doesn't have any holes because I was worried about dust and metal debris from my bench.3. Concerning TIP142 I'll consider it, thank you. What would you suggest as an isolation material? I wanted to try kapton.4. I didn't reach for help because I decided that if I start writing English there people wouldn't be happy. I'll come back when I learn some Dutch. I also decided that I can figure things myself. And I think I mostly succeeded, it works as designed and tested. I didn't reach my original performance goal (wanted max current 2A, but got only 0.9A before bridge rectifier starts to be uncofortably hot, then radiator serves up to ~1.4A at minimum voltage), but that's fine, I learn from mistakes. Next one will be better.So, yeah, it has flaws, but for me the most value is not in its performance, but in visual appearance and please of finishing the project. I use it every day to supply power for a sound amplifier. And I think it's coolPS did you notice that it has leds on front panel of different color? It was a whole week of work figuring out color scheme, ordering 13 different leds of different color and brightness, adjusting their current so they would visually appear at same brightness, making mate finish because leds I used had clear plastic forming a lens making a bright spot....

author: xavier60
author_rank: Super Contributor
timestamp: August 08, 2019, 08:08:28 am
content: I bread-boarded the CV loop using a TLC071 and a BD137 driving a TIP35C in place of the Darlington.There is some ringing during load transitions which may not be present in the original design when laid out properly on a PCB.I would still like to see it tested.It is much faster than the designs that I have been working with.

author: markce
author_rank: Regular Contributor
timestamp: August 08, 2019, 09:10:30 am
content: @xavier60I did a dynamic load test with my CO-2019 lab-supply. The load step is 0.2/0.8A,

author: blackdog
author_rank: Frequent Contributor
timestamp: August 08, 2019, 10:44:35 am
content: Hi xavier60,With a faster power transistor like the compound version as I have shown in several designs here on eevblog, the circuit becomes even faster.This is because the faster power transistors cause less phase shift.And yes, this is a pretty fast regulating power design.If a different power section is used, always check your two loop compensations.But if you need a capacitor that is more than 2 or 3 times bigger, you know that you are doing something wrong.Properly measuring the loop stability is quite difficult.And I mean how to connect electronics that will load your power supply dynamically and where to connect the scope (groundloop problems).There are many inductions involved, for example from your wiring and the ESR and ESL of the capacitor over the output of the Power Supply.With the CO-2019 Power Supply the measuring point is quite simple because it has two clear sensor wires.Where you connect the two sensor wires to the output terminals, you temporarily mount a BNC connector for your scope.5mm further and you're also measuring the induction of the wiring.Kind regards,Bram

author: exe
author_rank: Unknown
timestamp: August 08, 2019, 10:49:30 am
content: I'll test transient response when I'm back from vacation (next week). My expectation it should be good because, afaik, it's the forth iteration of power supply. So, I expect such issues to be fixed already. But who knows.One thing: I changed all caps to what I purchased separately. My output cap has much lower capacitance (and incidentally much higher series resistance) because PSU is mainly meant for breadboard experiments and I don'w want output cap to toast my incorrectly built circuits. So, measurements won't be representative for the original design.

author: blackdog
author_rank: Frequent Contributor
timestamp: August 08, 2019, 10:59:59 am
content: Hi exe,My output cap has much lower capacitanceOk, you are killing the performance of this design and it wil probely be instable now!Kind regards,Bram

author: markce
author_rank: Regular Contributor
timestamp: August 08, 2019, 12:35:08 pm
content: @Exe1. -2. Bridge rectifier, tranny and regulator circuit all generate some heat. With a self-made cabinet you could design some labyrint vent holes to release it.3. No need for expensive washers as long al you have small or moderate passive cooling. What is the size of your heat sink?4. Which type of bridge rectifier are you using, and what reservoir capacitor?

author: xavier60
author_rank: Super Contributor
timestamp: August 09, 2019, 01:59:37 am
content: Quote from: markce on August 08, 2019, 09:10:30 amIs there meant to be an attachment? , I think something is wrong with it.

author: markce
author_rank: Regular Contributor
timestamp: August 09, 2019, 05:23:23 am
content: @Xavier60Channel 2 (blue) is the voltage across the series resistor in the dynamic loadChannel 1 (yellow) is the power supply output (AC component).

author: xavier60
author_rank: Super Contributor
timestamp: August 09, 2019, 10:04:09 am
content: Quote from: markce on August 09, 2019, 05:23:23 amI see it now. My browser wasn't opening the link.www.circuitsonline.net/forum/file/43195That is an impressive result.With my recent project, the same test now causes a 140mV dip with 5µs recovery.I don't want to put a capacitor + resistor across the feedback divider resistor because of the way it affects voltage recovery after an overload.https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2388873/#msg2388873

author: exe
author_rank: Unknown
timestamp: January 11, 2021, 08:55:15 pm
content: My Dutch friends, I'm curious if there is voeding 2020 or voeding 2021 was released or planned. Do you have any information?

author: blackdog
author_rank: Frequent Contributor
timestamp: January 11, 2021, 09:21:55 pm
content: Hi,As far as I know there is no other Power Supply of CO.I do know that the builder of the previous version still has something in mind, but I don't know what kind of project this is.Because of Covid-19 there are no electronics fairs in the Netherlands and the new CO projects are mostly presented around this time of the year and then in the biggest electronics fair in March where you can buy or pick up the project.But that was not last year and not this year either....Kind regards,Bram

author: exe
author_rank: Unknown
timestamp: January 12, 2021, 11:23:45 am
content: Thank you very much for the update. I too missed the annual event at Autotron. That's where I bought my kit. I met the CO guys, it was fun.