Babbys (or, rather, chemists) first laboratory power supply unit - Page 1
Forum section: electronics / beginners

author: MaxFist
author_rank: Newbie
timestamp: February 11, 2016, 02:30:56 pm
content: OK so this is probably the millionth thread on this topic and I'm sure everyone is sick of people asking how to make a PSU.However! As a chemist I'm rather new to electronics, it simply isn't my forte (yet). So rather than designing one I was thinking more in the lines of replicating an existing design (maybe modify it a bit down the road). It beats giving 200+ euros for a decent factory made power supply!The power supply would be used mainly for diy electroplating, electrolysis and power supply for work in progress electronics builds. So it doesn't really have to be insanely powerful.For voltage output I was thinking something like 0 to 30V at most with <0.05 to 3A current. I was thinking of a simple knob operated action with a digital volt/current meter embedded, none of that fancy micro-controller doo-dads, that's a project for another time.As for the type, I'd go with linear because I'd like a low noise power supply.Regarding input... I still haven't decided to be honest. It really depends on the type of transformer I can get my hands on. It will probably be single, that's what I'll be going at for the moment.I've found some schematics online... like this one:http://www.electronics-lab.com/project/0-30-vdc-stabilized-power-supply-with-current-control-0-002-3-a/it appears to be perfect for what I needQuoteor this one:http://www.pocketmagic.net/variable-regulated-power-supply/although it's too powerful for my needs, but I reckon it could be fitted with a less powerful transformer and still do the job (perhaps do it better)I've also found this:http://lea.hamradio.si/~s55wt/Napajalnik_30V10A/Navodila%20za%20izdelavo.pdfIt's in german, sadly I don't understand german, but I kinda get what it's about. This one is 10A, which would be overkill again. Like with the previous one, I assume yo could just lower the input voltage with a weaker transformer (+ adjust all the high power components) and it would work just fine.Now I'd like to ask if these schematics are good, if they aren't just some shite put online by people who want others to burn down their houses.I'd be grateful for any input! If you know of any good schematics or advice, please share them it would help immensely!

author: Seekonk
author_rank: Super Contributor
timestamp: February 11, 2016, 02:47:02 pm
content: The second doesn't really regulate at the output. The 317 producesw a regulated voltage to the transistors but there could be a drop of up to one volt as current increases. That may not be an issue. There is a variation of this which uses PNP transistors that actually does regulate. LM317 circuits are very appealing to beginners but, they seem to be a problem for many here. I haven't used one in 25 years. They are just, close but no cigar.

author: MaxFist
author_rank: Newbie
timestamp: February 11, 2016, 03:20:59 pm
content: Quote from: Seekonk on February 11, 2016, 02:47:02 pmYeah, that does seem to be a bit problematic, would it work if you just transferred the regulator after the transistors?The second one also doesn't have a current regulator... would it be possible to add one?I've been seeing a lot of LM317 circuits for PSU's, can you replace it with something better without changing the circuit much?

author: Seekonk
author_rank: Super Contributor
timestamp: February 11, 2016, 03:43:28 pm
content: The LM317 sounds ideal, a transistor, op amp, and voltage reference in one package. Trouble is once you go beyond 200ma a lot of stuff needs to be added. Add all that stuff and you might as well build one from scratch.

author: Morgoroth
author_rank: Regular Contributor
timestamp: February 11, 2016, 04:26:20 pm
content: power supply are not so simple, and you need some decent instruments to test it properly, better get a decent/cheap one and focus your efforts on a current control for your electroplating and electrolysis projects.And could be dangerous too.eBay auction: #http://www.ebay.com/itm/Adjustable-Variable-Precision-Digital-LED-Regulated-DC-Power-Supply-30V-3A-4AO5-/131681897695

author: Audioguru
author_rank: Super Contributor
timestamp: February 11, 2016, 04:41:38 pm
content: The first circuit from Electronics Lab is full of errors. Many of its parts are overloaded including the transformer, output and driver transistors and opamps. I fixed it in their forum.