DIY Variable power supply - Page 1
Forum section: electronics / beginners

author: chiken
author_rank: Contributor
timestamp: March 20, 2019, 07:30:35 pm
content: Hello everyone,Having Power supply with variable voltage and current would be quite hand to me as a student so i wouldnt fry things every so often,and since my attempt to buy cheap Variable Psu has failed, and trying to fix chinese boards failed even moreI decided that it would be best to build it myself.And since I did not reach that level of education to be able to make schematics that far myself, but am able to understand already made schematics,Is there any fellow forum colleague who would share some schematics of PSUs with variable voltage and constant current for educational purposesI was thinking about 30V and 10A what would maybe be overkill, but that is pinnacle, 5A would be fine, but wouldnt go lower than that, Voltage 20V+...And if anyone is wondering why would i give that much effort in it and simply not collect some money and buy one for 50$ from amazon, well few reasons why :1. i like to make things myself2. as a student, budget is stingy..3. as i said, ive already tried buying one, even though it was lot cheaper, but wouldnt risk buying chinese crap again4. if i have to choose between buying something for 20$, and buying parts and making it myself for 20$ without thinking would choose 2nd option,as i said im student and making it myself would vastly help me understand principles of it and maybe one day create one myselfIf is there any other place that i could post like this, please let me know.Critics somewhat allowed, just dont go berserker please hehe

author: RES
author_rank: Regular Contributor
timestamp: March 20, 2019, 09:02:35 pm
content: Low count, discrete standard parts, you can think of a supply like this. (no current control)

author: chiken
author_rank: Contributor
timestamp: March 20, 2019, 09:31:16 pm
content: thank you for your reply,but i didnt mention that constant current, current control is quite necessary

author: xavier60
author_rank: Super Contributor
timestamp: March 20, 2019, 09:31:35 pm
content: There are 2 threads currently with working designs.https://www.eevblog.com/forum/projects/linear-lab-power-supply/msg2272788/#msg2272788https://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/75/

author: rstofer
author_rank: Super Contributor
timestamp: March 21, 2019, 02:13:14 am
content: Read through the linked threads above. You will find that building a lab supply with your requirements is a really big design challenge and many hobby circuits have warts.Search through this site, Dave did some videos on switching power supplies with nice digital displays that are only $20 or $30.https://www.eevblog.com/2017/10/11/eevblog-1030-20-diy-bench-power-supply/Search for othershttps://www.eevblog.com/episodes/

author: exe
author_rank: Unknown
timestamp: March 21, 2019, 07:54:30 am
content: Well, you can just chain two lm317, one for current control, another one for voltage. A more sophisticated design is like this:http://www.paulvdiyblogs.net/2015/05/tuning-030v-dc-with-03a-psu-diy-kit.html. There is plenty of discussion of this PSU. I'd say it's good start, but you do need to understand that maximum specs are a stretch. A bit hard to understand how it works in details...There are a few books and articles that are worth reading. Start with this:https://www.hpl.hp.com/hpjournal/pdfs/IssuePDFs/1962-07.pdf. Then read stuff here:http://sound.whsites.net/articles.htm#psud(esp. about component sizing). Also watch Dave videos mentioned above.A few examples of power supplies for design inspirations.Here is my attempt to build a psu, it works great last three years or so:https://www.eevblog.com/forum/beginners/please-critique-this-linear-psu/. I think I amended schematic a little bit after posting, so, use with caution. Really fast PSU (thanks to lt3080). Min voltage on mine in CV mode is about ~0.7V, good-enough for me. CC goes to 0.There is another psu I bumped into, seems to be interesting (use google translate):https://www.circuitsonline.net/forum/view/144222.This one is my favourite so far:https://www.eevblog.com/forum/beginners/how-does-blackdog_s-psu-work/.All those are linear psu. It can also be an smps, it can be hybrid, etc.And last but not least: mains are dangerous, be sure you understand basic safety concerns and circuit protection.

author: chiken
author_rank: Contributor
timestamp: March 21, 2019, 10:49:36 am
content: Sorry if im wrong, but this cheap thing from aliexpress ()does not look complicated at all, yet says 3AMPS max, so why would 5 or more amps be such a problem

author: exe
author_rank: Unknown
timestamp: March 21, 2019, 11:31:41 am
content: It doesn't really matter what's written on it. The limitations are 1) power dissipation on pass transistor 2) pcb traces 3) if pass transistor has enough gain at required voltage.You say you need 5A-10A. May I ask why? I feel like the number is a bit random. Anyway, I'd start with more detailed specification including efficiency, noise, and size. And I'd be practical about it. I know that 5amps is "nice to have", but 99% of time my 1A power supply is enough. If need more I simply connect two channels together. I'm also not sure how much 20V+ is needed. I'd say voltages beyond 12V are rarely needed. Many times I could supply a 15V+ device from 12V. I mean, there are use-cases when you may want more than 12V, but be sure you really need this.People often have two power supplies: one is "low-power" linear, and another one smps for high currents.

author: chiken
author_rank: Contributor
timestamp: March 21, 2019, 11:57:27 am
content: Well im not yet in that much fine electronics,I someqhat repair consumer electronics and it would be useful to be able to test motors(usually up to 30v) and led diodes(again up to 30v),Well they ofeteny go up to 5amps but it would be nice to always have 5 amps to spare and/or charge some batteries,Thats why i want to make it myselfI doesnt have to be ultra fine and precise but juat Ble to do the job

author: iMo
author_rank: Super Contributor
timestamp: March 21, 2019, 12:32:56 pm
content: Another PSU people elaborate just now is herehttps://www.eevblog.com/forum/projects/bench-cccv-psu-based-on-daves-usupply/And the Xavier60' one simulates fine as wellhttps://www.eevblog.com/forum/beginners/lm324-power-supply-with-variable-voltage-and-current/msg2279676/#msg2279676

author: exe
author_rank: Unknown
timestamp: March 21, 2019, 02:07:11 pm
content: I can't really suggest anything. I could recommend this one:https://www.eevblog.com/forum/beginners/how-does-blackdog_s-psu-work/msg1456590/#msg1456590. But it can be too complicated.May be the best approach would be to start reading literature, do own research, build a few less biffy power supplies, learn from them and then build the one you want. Just keep safety considerations in mind. Also heat dissipation, etc. Usually, the problem is not to output 30V 5A, but, say 1V 5V because of drop out on the pass element (unless it's an smps, which is probably better for your case). Understanding where and why heat is dissipated is crucial. As well as thermal performance.Alternatively, you can just buy an isolation transformer, beefy diode bridge, a big capacitor, and a ready module. May be a soft-start circuit if transformer is too beefy.

author: castingflame
author_rank: Regular Contributor
timestamp: March 23, 2019, 04:49:32 pm
content: Could you use a PC PSU and and so.e front end to it?Sent from my SM-N960F using Tapatalk

author: rstofer
author_rank: Super Contributor
timestamp: March 23, 2019, 05:44:26 pm
content: Quote from: exe on March 21, 2019, 02:07:11 pmThat's quite a transformer. Yet this kind of thing comes up all the time. It is very difficult to design a PS that can deliver 30V 5A and also deliver 1V 5A without a tapped transformer and some kind of winding selection.We need power sources for the op amps and here they are created from separate windings. Nice!That schematic is dumbed down according to the author. It clearly shows why bench supplies are not cheap!It's no big deal for a manufacturer to get a transformer with multiple secondaries. It is particularly easy with toroidal transformers. It is somewhat more difficult for the DIYer.

author: exe
author_rank: Unknown
timestamp: March 23, 2019, 06:20:48 pm
content: Quote from: rstofer on March 23, 2019, 05:44:26 pmHuh, yeah, that circuit was simplified in two ways: no active rectifier (lt4320), and no pre-regulator. With that pre-regulator multiple taps are not needed. The pre-regulator can be found here:https://wahz.blogspot.com/2015/10/lab-power-supply-project-pre-regulator.html. There is also a discussion of it on this forum, but I wasn't able to find the topic.I built one power supply with two channels using that pre-regulator, seems to work well (with toroid 30VA). My next build is a psu with 120-200VA.

author: Rick Law
author_rank: Super Contributor
timestamp: March 23, 2019, 11:53:32 pm
content: Quote from: chiken on March 20, 2019, 07:30:35 pmBold and underline added to quoted postFrom one amateur to another...I suppose you are aware thateven if you made it yourself, chances are, you would need to do quite a bit of debugging with it also, perhaps even more debugging than with a purchased board.As an inexperience person myself, I know that after soldering something together, the joints may not be correct, the components could have been overheated, component could have been inserted in reverse... etc., etc.With a DYI, you are more on-your-own with your one of a kind. With a purchased board, there is a higher probability that at least the board should work. There is a hope that someone else may have the same board and can render advice with that specific board. For example, here with the B3603 digital buck PSU, we have a nice lengthy discussion helping each other modify/find problems:https://www.eevblog.com/forum/reviews/b3603-dcdc-buck-converter-mini-review-and-how-the-set-key-could-be-fatal/Perhaps get a cheap board (30V 1-2A) for your initial need to start. Separately do few simple linear regulated ones to learn; then do a few boost/buck switcher to learn; then attack a real adult size 5-10A supply that you want for longer term.I've to say, tearing down a load (dozen or so) of PSU boards and "car phone charger adapters," I learned a hell of a lot - enough to make a couple that I could use as my "main" project PSU's on my work bench . But, I ultimately continued to use the B3603 as my "bench supply" because home made ones just isn't as nicely packaged.

author: not1xor1
author_rank: Frequent Contributor
timestamp: March 24, 2019, 08:33:33 am
content: Quote from: chiken on March 20, 2019, 07:30:35 pmyou might buy those cheap linear Chinese PSUs...You should find 0-30V 0-5A new units around 50 €.Then you have to fix:- the transformer (usually nuts and bolts lacklocking washersand are lose)- put a real heat sink (TME has a good and cheap one for 2 TO3 BJTs)- change some electrolytic capacitor (those at the input filter are 50V unknown brand - you might use 2 samwha 4700µF 63V)- change the rectifier bridge with a more beefy one (10A or more)- optionally improve air flow- do not use it continuously above 3-3.5A

author: eletronob
author_rank: Newbie
timestamp: March 29, 2019, 07:47:40 am
content: Quote from: not1xor1 on March 24, 2019, 08:33:33 amWhat is TME?

author: Shock
author_rank: Super Contributor
timestamp: March 29, 2019, 09:15:36 am
content: Quote from: eletronob on March 29, 2019, 07:47:40 amEuro parts distributorhttps://www.tme.eu

author: Jwillis
author_rank: Super Contributor
timestamp: March 30, 2019, 12:53:16 am
content: Quote from: chiken on March 20, 2019, 07:30:35 pmBuilding your own is the best part of learning. Anyone can just go out and buy a power supply or a few pre-built circuit boards and connect them together but you learn nothing.The hardest part is finding something on the net that is tried and true and sifting trough the garbage to find something that really works .Out of the ones that really work , its hard because the lack of available parts or the shear complexity just makes them cost a fortune to put together.These two have fully adjustable voltage and current .One is based on the LM723 which is readily available and inexpensive.The other is base on the now obsolete MC1466L/MC1566L.The MC1466L can be built that uses common discrete s if you can't locate the chip. Or if you are really ambitious a circuit exists using SMD. Both circuits are fairly stable and inexpensive to build.Also theirs a lot of information available to help with many questions you may have.Lm723 variable power supplyhttps://www.airspringsoftware.com/p/1549767647173118/or herehttp://www.classdaudio.tk/index.php?page=3010I'm not familiar with this one but I'm sure you can get help on it if needed.MC1466L/MC1566L variable power supplyhttp://chemelec.com/Projects/MC1466/MC1466.htmor with the SMD version herehttps://hackaday.com/tag/mc1466/Getting the MC1466L SMD boards is easy and I picked up 6 for about 14 dollars US found herehttps://oshpark.com/shared_projects/tU1Dv8o4I built this one and it works great.The only problem that popped up was the voltage control potentiometer needs a small resistor between the wiper and ground instead of being directly tied to ground.Hope this helps some.