VoltLog #8 - Kit Assembly 0-30V 0-3A Adjustable Linear Bench Power Supply 

thank you!

John, , look up Practical Electronics October 1978, it contains the original design…

awesome tips, thanks!

I assembled this power supply and supplied the AC input via 12*2 3A (Centertapped Transformer) but unfortunately there was no correct output at the output terminals; it's almost 0.3V DC. But when I checked the 82 ohms resistor which is near to the reverse diode capacitor multiplier (17.36 in this video) gets much hot. I checked all the directions and components but still it's not working. Can someone help me to solve this issue?

@@JohnWick-pz5vp When you pause video on the diagram 16:59 you can see that the 82 Ohm (R2) is in series with 47 uF (C2) capacitor, so this should not get hot at 60 Hz. Perhaps the capacitor 47 uF (C2) got shorted? Replace it and see what happens. Also, the center tap of the transformer has no meaning in this circuit. The 3-screw input terminal has the center screw not connected to anything. Measure the AC Voltage on the two outside pins: it should be around 24 Volts AC, but the circuit will work fine from 8 Volts AC and up.

@@JohnWick-pz5vp Yes that resistor does get hot...but it works OK anyway. You probably have a bad TL081. Either order more (I got 50 for under $10 from a US seller) or use the UA741 as someone else has suggested. Oh and buy some sockets for the opamps, so you can change them easily if you need to! I ALWAYS use them now. Be very careful desoldering the opamps or you will lose the traces on the board.

I built same aliexpress Board. Worked with ac transformer, after some time fried tl081 on the right. I did not used diode in place of zener. What could be the reason of fried op amp?

zooky443 I'm glad my story helped.

+gowhar khan Thanks! You cannot increase the output current by using two power supplies you will run into problems, voltage sources should not be paralleled. The voltmeter should be connected to the output terminals and the ammeter in series with the output terminals. I would recommend using a 10 turn pot, it's nicer. Also there is a really long thread full o information and possible improvements to this power supply, you should read it. Here is a link voltlog.com/y/bmdio

Thank you for sharing the technique with us. I am using the exact same technique as described in your comment. However I have to disagree on the part where you say "you don't need much flux", extra flux is always helpful even though I am using solder wire with flux core. It just makes your life easier, why should I stick with just the flux I get inside the solder wire? that's not enough. Sometimes the core melts on the current joint more than it should and to your next joint you are left with only bare solder. The thing that gets you most of the time during soldering is oxidization of the solder on the tip or the tip itself and flux together with regularly cleaning the tip is a perfect solution for that. I have to conclude though, this is a rather "personal" subject as everyone does it their way, and everyone has their own sweet spot for how it should be done.

True, I usually use flux when I get a failed bead to touch it up. Saves time and flux. Since most connections are easily done without extra flux.VoltLog

Mtaalas ,There use to be copper wire coat with silver for easy solder as time pass they change from copper to brass. now some Electronic parts from china use steel wire coat with may be nikle. Part from china are very difficult to solder that why I understand he use too much flux. Too much flux quickly ruin your platinum coating on soldering tip. I always avoid buying part from china.

A bit of added flux always helps. I normally do my solder junctions in less than 2 seconds, with a very hot iron (380ºC) to improve wettability. The flux from the solder wire might not be enough. It is preferable to err on the side of caution and clean the excess later. As long as you don't use conductive or acid flux, you'll be fine.

usually you don't go below 10K with adjustment pots. It should still work but I have no idea if it's going to influence your circuit in any way.

+Anjay V Reading the manual there is no mention of short circuit or reverse polarity protection? Of course, it's not a detailed manual so?

+Sylvain LAZARE I don't recommend using that transformer. When rectified the voltage could exceed 40V and the power supply components are not rated for that.

yes

Exactly why i tested 12-0-12 transformer gives 40v on the caps. My Opamp Fried after some time. We should use 9-0-9 transformer.

@@ajaybnl OMG I JUST FOUND AN 18V 40W TRANSFORMER THAT CAN SUPPLY 2.25A max. (from a broken boombox) I only need ~ 3A up to 12V, not more :) So I'm GOOD TO GO!

Just get another kit off ebay....for $4.50 how could you go wrong?

Thanks! I definitely recommend building this power supply.

+Cagri Coskun If I remember correctly that is the 0V adjust pot.

+VoltLog thanks

Hi, thank you for watching!

+Alex Tomin here's where I get it from

the only one I know of.

You can just screenshot the video for schematic

Here: imgur.com/a/3N58n9k To do it yourself, PRT SCN top right of keyboard, then CTRL + V into paint and save as PNG

true, but the 7824 is not critical, it is there just to offer a 24V rail for a fan or to power something else external.

@@voltlog to make it look neater and more professional by having the cooling fan connected to the unit... And not to a separate unit

I'll be replacing the 7824 with a 7812 cuz I don't have 24V fans, and the case I've prepared has a 12V fan built in so 7812 is mandatory

COJEIGUEN HERTRANKA It will not work with DC voltage. As I've explained in the video it needs AC voltage for proper operation.

You don't think this kit is worth it for $4.50?

Yes, i believe you can

Digger D right, you would have to test dissipated power vs resulting temp. It is a fun kit for sure! :)

I will probably run it at only 1.5 to 2 amps as I think that is the limit of my transformer so likely the case will do as a heat sink. How do you find the pots for adjusting, would 10 turn be worth while (I suspect so).

Digger D 10 turn for the win! If you're considering using this as a lab power supply you will appreciate the finer adjustment into the mV range or mA range.

I thought so -thanks.

the trim pot is for 0V adjustment.

Got it !!! Thanks !! {:>)

@@voltlog mine is right at 0 volts right out of the factory

it will work at that voltage as long as it's AC.

Tyvm :D Will try it out tonight then.

+George Tsiros No, I haven't. I plan on mounting this thing inside a case soon and I will probably do some tests when it's finished. Do you have reasons to believe it would not behave correctly ?

+VoltLog Yes. Check tl081 supply rails in the circuit and from the datasheet. Do me a favor, slap a sink on that 3055 and a 24v secondary transformer and test the circuit's behavior when the current setting is very close to the current through the load.

+VoltLog Also check for oscillations and ripple voltage as well.

Great advise!

Feri Beke not really short circuit protection but it has CC mode which will limit current based on your setting. I haven't had issues with this power supply and I've short circuited the output many times.

yes you can, but you should not. . The opamps have a maximum voltage of 30v. After filter, a voltage of almost 34 volts apear. Under load, I'm sure it is not a issue, but I let mine powered on over night with no load and burn the opamps. This power supply shoud be ratated maximum to use with a 20v transformer. 12 0 12 or 24 0 is too much for this supply.

+Cezary Siwek - It won't work from a single DC supply, it needs AC or the charge pump circuit that generates the -5V rail will not work. To use DC you'd need to also supply the -5V rail, ie a split rail supply. The designers made it like that to keep things simple for the kit builder.

ProdigalPorcupine designer did not design this kit like that way, they have just copied famous linear cc cv power supply schematic and made a kit out of it. And yes you are right , one need to supply negative voltage tot the circuit while operate it with a dc supply. But split rail supply is hard way to go but icl7660 is neat charge pump with its several cents price tag:)

Did you set the CC by shorting the leads first? It does work...at least on my kit.

I have just finished assembling this kit into a complete unit with enclosure. I did a couple of measurements and I need to make some improvements. I will do the improvements and the measurements in a future video.

VoltLog I am at that stage right now just putting it all in enclosure. Not a lot of capacitance for a 3 amp load.

VoltLog So do I wait for the video for feedback?

I'm waiting for some parts to be delivered before I can start preparing the video, it might take a while.

I would be surprised too if my cap would be from "nichicin" :-)

nichicon I meant xd

Mine is made by Chongx :/

You are crazy overkiller. There is no need for second and even third transistor, just good cooling at it will be ok. Also 100W good quality transformer will be ok, we dont need 50% margin.

At uni we were taught to aim for 10x over specification if possible. A 100ma circuit use 1amp parts. It is all about reliability, longevity and catering for the variation in component quality. I finished this supply and used two transistors. However I paralled the secondaries to give 12v at up to 12amp. The worst case 3amp temp of the large 2.2c per watt heatsink is 96c. ( 191c for a 30v supply). The transformer is stone cold as is the internal circuit. Good safety margins means I have screwed the case shut and never expect to have to open it for repair.

I also use 1A diode with current at 100ma, because package and price is same. But 10x more that needed in many cases is ultra overkill, I never heard something like that. With two transistors and 12VAC/24VAC tap switching we could run at 8A... Or if we are going to build 3A linear psu its good to use 4700uF main cap, or two 3300. But 30mF cap(10x than minimum) is absolute overkill for 3A psu -,- I know what im talking about, I have expirience, I work in high-end goverment/military grade access electronics production.

that's a 1.66A rated transformer

Thank you for replying! I have couple of stepper motors that I want to run at 24 volts. Does that mean that I can have only 1.66A total current from the power supply? I mean 24 vac must be rms value so the peak value would be 1.414*24 i.e. 34v. Now we are stepping it down to 24 volts so the final output will be able to provide more than 1.66A dc.

I'm using a 24V 48W transformer, since I don't need 3A across the voltage range But still 16 volts and below - 3A

+SidneyCritic ComedyHound yes it will work with 12V AC.

+VoltLog Great, that will save me some money. $15 for the kit, and $40 for 24V AC transformer, wouldn't make it cheap. I can't find the specs on the EI-40c transformer, so will have to test it, but there is also something in the PS that looks like toroid. I'll have to investigate. Thanks

+SidneyCritic ComedyHound Here in Romania, a 24V 2A toroidal transformer is about $15 and a used one could probably be purchased for less. Wherever you are from I am sure a cheaper transformer can be found. ATX PSU do not contain toroidal transformers. And the other transformers contained in an ATX PSU are most likely not suited for this job.

+VoltLog I just found one at $18 on eBay, but when you add the circuit($15) and a volt/amp panel meter($8) it comes out at $41, so I was trying to cut costs in half with the ATX PS parts. I've got a failed ATX PS with lots of transformers, and the biggest is a EI-40c, but I can't find exact specs. Maybe this www.kondzio.info/images/artykuly/2015/transformator-impulsowy/EI-33-datasheet.pdf chipsen.en.made-in-china.com/product/IBZJxAPdgnWk/China-EI40-Current-transformer-specification.html Here are some pics www.mediafire.com/convkey/5cfc/snsaot1xhjknz3b6g.jpg www.mediafire.com/convkey/c141/4uva5mjt899iyto6g.jpg www.mediafire.com/convkey/edff/z66lnkp4g9f05jd6g.jpg The gutted ATX case has a 12V fan, 240V connections, switch, and what I think is a filter inside - cap and inductor -, so it's ready to populate. Any advice would be appreciated. Thanks

+SidneyCritic ComedyHound The PSU KIT is $10 goo.gl/3r5YKl , you will also need a heatsink.

Matias Cueto Hello friend. Have you solved this problem, because I have same issue with 24v 4a AC transformer. Getting only 0.614v at output. Thanks.

Ola amigos I got same issue.til now searching for answer

Sure it won't be capable to dissipate the heat generated from a low voltage high current output setting but that's not a common situation. It would probably be ok for a a couple of minutes and if you really need that kind of setup often you probably need a more specialized bit of gear. For the average hobbyist this will do fine.

Well, IMHO, this supply is overrated. It should be limited to just 1A and the voltage of the transformer should be halved. It would still be a useful supply, but this would ensure that it always operated safely and well within specs. For instance, I designed a 200mA precision supply where the pass element is a MJD31C (the SMD version of the TIP31C). Mind that this transistor is rated for 3A. This may seem overkill, but you have to take SOA into account. SOA considerations apart, this supply seems to be well designed and will do the job. It doesn't have to be a super top-of-the-line supply, I agree on that. Unlike Dave Jones, I don't roast a product just because it is affordable instead of lab grade.

P.S. Do NOT solder in the TL081 opamps as you will have terrible trouble desoldering them if they blow up......just order some sockets for them instead.

@@englishrupe01 Okay, I will try to find some IC sockets.... I can salvage them from old PCBs I don't want to wait for the shipping

@@adamsucksatyt Cool....yep i understand your enthusiasm...you will thank me later though, lol! I am sure you will love these kits and order more. It is also important to use a heat sink. If you do order sockets, i find the ones with round holes are much easier to use too. Good luck...oh and Amazon sell these kits cheaply too (fast shipping!).

There HAS to be a way to make it work on DC

+Daniels this power supply kit only works with AC at its input.

Probably a bad TL081...swap them out after putting them in sockets.

#englishrupe01 No negative voltage on IC pin 4 means there is possibly something wrong with the voltage inverter for the op amps Maybe a faulty component? ------------------------------------------------------ :( Your PC ran into a problem that it couldn't handle, and it needs to restart. We're just collecting some error info, and then we'll restart for you. (-1% complete) If you'd like to know more, you can search online later for this error: ADAM_SK_EN_FATAL_ERROR

I have a 24VDC power supply at home, but I don't have a 3A 12 - 0 - 12 transformer or even a 3A 24V transformer Damn it

That is definitely a bad TL081. I advise anybody assembling these to fit the TL081's in a socket first....otherwise it is very difficult to remove them later....and since they are pretty much at their limit anyway, it pays to have a few spares on hand. I bought 50 for around $5 i think....and the sockets are very cheap too.

I made three of these kits and one was completely duff. Same symptoms as you. There are a fake or low spec TL081's out there, they have a 'V' type logo on them, I bought 5 of them to replace the hot one. Should have got genuine TI chips. None of them worked. If you get the circuit diagram and assemble U1, D8 , R4, R6, R5, P1 with DC anywhere over 15V you will get about 10.2V at U1 pin 6 and 5.1V at pins 2 and 3. U1 works as a voltage reference and the voltages I listed will be present for any DC supply voltage above about 12V. The TL081's in my duff kit and the 5 I bought off eBay did not work in this circuit, the output voltage on pin 6 was stubbornly 0V. I made a circuit in LTSpice XVIII and no matter what values of R4-R6 I chose I could not get 0V on pin 6, it worked as theory would suggest and as per the good good boards. This and the two good boards showed me where to look, having eliminated everything else I concluded the TL081 was not working as it should. In addition pin 8 was not NC, it was at Vcc. If you short pin 8 to Gnd the chip dies. I dropped in 741's instead of TL081, they are pin for pin compatible, and it worked. I put sockets on all IC's. Blown also was U2. R1 and R2 run hot to touch, they need to 1W I suspect. I replaced all TL081's on the duff board with 741's. The good boards have genuine TI chips. This solution took a long time to figure out.

Sorry, I have no intention of upgrading my power supply to 5A but here is a forum where allot has been discussed about this power supply: electronics-lab.com/community/index.php?/topic/26825-0-30-vdc-stabilized-power-supply/

Here is the video with the enclosure build ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-_jd4waHxJYs.html

you could do that, but you need to install it on a heatsink, depending on the power draw of the fan that regulator will get hot.

First check that each component is correctly mounted on the PCB, next make sure you use AC input.

Thanks, think my issue was finger trouble. I got it to work, but R2 still gets pretty warm. If that's normal I just leave it as is and start building it into a box. Thank you for the advise

R2 should not be warm, I can't check right now but I don't remember that resistor getting hot on my build.