Recommendations for a beginner bench power supply project? - Page 1
Forum section: electronics / beginners

author: microbug
author_rank: Frequent Contributor
timestamp: April 28, 2013, 05:09:13 pm
content: Hi,I don't have a bench power supply yet (I'm saving up), but in the meantime I thought I'd make a basic bench power supply (using a LM317). I have a fairly basic understanding of electronics, so I also thought this would be a good opportunity to learn some more.My first question is whether I need a CC / CV power supply or just a CV. Personally I would like to go for CC / CV, because I sometimes have a need to keep current limited when working with lasers, but this isn't really necessary as I have separate laser drivers. I mostly work with small battery powered things at the moment (I'm currently making a portable USB charger running from 2 3.7v 18650 Li-Ion cells), so I usually don't need more than 10 - 15v in power.I understand that the LM317 is a good choice for this sort of application, but I am open to any other suggestions. What I need is a schematic that has more detailed information about components than most - e.g., the voltages of capacitors - because I usually don't know what sort of values I would need if they aren't printed.I do have some experience with dealing with high energy circuits (although not the mains), so I wouldn't mindtoomuch dealing with the mains, however I'd prefer not to - maybe I could use a plug-in adapter/transformer to power it?Thanks in advance!

author: Alana
author_rank: Frequent Contributor
timestamp: April 28, 2013, 05:32:34 pm
content: If you want linear PSU with CC/CV capability look for L200. I think this picture is from one of datasheets:http://obrazki.elektroda.pl/7582279200_1309598107.jpgAdditionally - L200 has 2A max current and this may be usefull. But if you need just 1A CV supply stick to LM317 - they are fool proofAnd for rest of your information look up for "linear psu design" on google or youtube. For examplehttp://sound.westhost.com/power-supplies.htm

author: microbug
author_rank: Frequent Contributor
timestamp: April 28, 2013, 05:45:52 pm
content: Thanks! I think I will go for a CV only circuit for now, I found a good onehere. I would usethisone, but I can't find 47r potentiometers anywhere!

author: Bloch
author_rank: Unknown
timestamp: April 28, 2013, 06:05:07 pm
content: Quote from: microbug on April 28, 2013, 05:45:52 pmThat´s weird[size=78%]http://www.digikey.com/scripts/dksearch/dksus.dll?FV=fff40004%2Cfff80335&k=Potentiometer&vendor=0&mnonly=0&newproducts=0&ptm=0&fid=0&quantity=0&PV1=1113&PV1=1208

author: mariush
author_rank: Super Contributor
timestamp: April 28, 2013, 06:49:37 pm
content: Or you could put a 47-56 ohm (fixed resistor) in parallel with a 500 ohm potentiometer (you can find cheap 11-24 turn trim pots, they're about 2$).This will give you a resistor with values between 0 and about 50 ohm , so basically a 47 ohm pot.1 / Rtotal = 1 / R1 + 1 / R2 , this is the formula for resistors in parallel.Though, I'm not sure a trim pot can tolerate the current in that section of the circuit, the circuit is probably designed for one of those big 47 ohm potentiometer with knob. Might find

author: Alana
author_rank: Frequent Contributor
timestamp: April 28, 2013, 08:04:57 pm
content: This pot between 5 and 2 pin of L200 is current shunt and will burn if more than few mA passes trough it. If you want to use this kind of idea use switchable fixed resistors of proper power ratings. This is the reason my circut has op-amp - to keep high currents away from pots.

author: hlavac
author_rank: Frequent Contributor
timestamp: April 28, 2013, 08:36:38 pm
content: Current limit is extremely useful. When powering stuff up for the first time it may save your circuit when you made a mistake and shorted something out...

author: ptricks
author_rank: Frequent Contributor
timestamp: April 29, 2013, 12:19:08 pm
content: You could make a select-able voltage supply, would need a rotary switch with 4+ different selections and put the correct resistor for the voltage on selection., you can just turn the knob and get 2.1,3.3,3.7,5.1 etc every time without having to dial in a specific voltage using a pot.You can do the same thing for current limiting, using resistors in series with the supply output.

author: Jeff1946
author_rank: Regular Contributor
timestamp: April 29, 2013, 07:00:37 pm
content: A laptop power supply makes a simple front end for your system, typically they produce about 20V and 2 to 3V. Often you can get them for free from folks with failed laptops.