power supply kits and schematics - Page 1
Forum section: electronics / general

author: Unknown
author_rank: Unknown
timestamp: February 10, 2012, 01:33:05 am
content: I have been looking around for quite some time to build a bench power supply. I have found kits and schematics but I am not sure of the reliability of them. So that is when i thought to myself and realized why not ask the EEVblog forum. There is plenty of experience there, I'm sure someone will know exactly what I need.I am looking for these specs.Constant current control and constant voltage0 to +- 10V0 to 1.5 AWhat have you had success with?Any good deals on kits?

author: caffeinatedbard
author_rank: Regular Contributor
timestamp: February 10, 2012, 01:39:25 am
content: Hey,I would check out the power supply series that Dave is currently working on on the videoblog site. I think it fits your requirements.Good luck!

author: Unknown
author_rank: Unknown
timestamp: February 10, 2012, 01:46:20 am
content: Believe me, that was the first place I lookedHis is only going to be 0 to +6 V and 0 to +1 AI am looking to have -10 to 0 V and 0 to +10V with 0 to 1.5A

author: grenert
author_rank: Frequent Contributor
timestamp: February 10, 2012, 03:20:04 am
content: Finding a kit that goes down to 0V is going to be hard to do.If you can live with a minimum of around 1.25V, the Elenco XP-720K is a nice project. The manual says it outputs 1A for each rail, but the design is LM317/LM337, which typically put out 1.5A. Replacing the stock pots on that kit with 10-turn ones will give you finer control of the voltage setting.Here's some info:http://c0nsumer.livejournal.com/836691.htmlhttp://www.n5ese.com/xp720.htmhttp://freezerdev.blogspot.com/2011/11/elenco-xp-720k.htmlIt's sold by a lot of places, this seems to be cheapest:http://www.testequipmentdepot.com/elenco/power-supplies/xp720.htm

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 10, 2012, 03:51:53 am
content: The Kit that Dave is working on can be easily modified to fit your specs. You would only need to modify the input voltage and the op amp gain resistors to go up past 12V. The LT3080 can only push 1.1A, but the LT3083 can do 3A. So with minimal changes, and swapping the LT3080 for an LT3083, you can have up to 3A and up to around 18V. (Although, the higher the voltage you go, the more load on the regulator at high current and low voltage applications.)If you build two of these, you can have two supplies or join Pos to Gnd and get your +/- voltages for op amp work. You just have to use isolated feeds for the power.I will be working on very similar mods eventually. However, there are tons of Honey Do projects in front of that.

author: amspire
author_rank: Super Contributor
timestamp: February 10, 2012, 04:12:16 am
content: Quote from: sacherjj on February 10, 2012, 03:51:53 amWell, not really. The LT3083 has the same problem as theLT1083LT3080- it can only dissipate a modest power.If want a supply to operate up to 40 deg C, and you do not want the junction to go above 100 deg C (the absolute maximum is 125 deg C and running it near maximum is bad for reliability), then with a 2 deg/C heatsink, you are limited to a power dissipation of 12W. That means at 1.5A output, the maximum supply voltage to the power supply is 8 volts. So this means you would end up with a 0 - 7V , 1.5A power supply. 18V at 3A output? If you had a heatsink permanently cooled to the absolute minimum temperature of the industrial grade LT3083 of -55 deg C, you could possibly make a 3A 15V.Richard.

author: electrode
author_rank: Regular Contributor
timestamp: February 10, 2012, 04:38:49 am
content: Quote from: sacherjj on February 10, 2012, 03:51:53 amAre there any pitfalls with taking the output of two isolated supplies like Dave's and connecting them in series and/or parallel? I'd imagine parallel would be harder, especially if one supply was trying to output a higher voltage and the other supply acted as a load...

author: damo
author_rank: Contributor
timestamp: February 10, 2012, 05:57:51 am
content: If you base it on the lm317, you can place 3 suitable diodes (e.g. 1n540x) on the output to reduce the output to 0V when set to minimum. Here is a 6A design from 0-28V which you could modify to your specs. Use the centre tap of the transformer for your 0V and use a combination of lm317/337 as regs. Are you any good at converting a circuit from a negative ground to a positive ground?Edit: forgot the linkhttp://electronics-diy.com/power-supply-lm317-2n3055-0-28v-6-8a.php

author: Unknown
author_rank: Unknown
timestamp: February 10, 2012, 06:29:58 am
content: Quote from: damo on February 10, 2012, 05:57:51 amWOW... I like this design a lot actually. Thanks, with a few mods i think this might be it unless something else sparks my interest

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 10, 2012, 06:09:13 pm
content: Quote from: amspire on February 10, 2012, 04:12:16 amGood analysis. Thanks for that. There doesn't seem to be much advantage of the 3083 then. You could parallel the LT3080 to get nearly double the current, correct? (This is assuming enough thermal separate thermal cooling obviously.)Quote from: damo on February 10, 2012, 05:57:51 amUnless I'm missing something, I think you would also need to add a current limit, if you want that. I think it is almost required for a lab supply. I would have melted many less breadboards with that as a kid.

author: amspire
author_rank: Super Contributor
timestamp: February 10, 2012, 11:14:23 pm
content: In my opinion, you need to add current limiting to LT3080/3083 or even LM317 based circuits.Both chip have thermal limiting, but it is designed for short term protection only. The maximum continuous junction temperature for both devices is 125 deg C, and yet in thermal limiting mode, the junction temperature exceeds 160 degC.If they fail, they will short dumping the full input power onto your load.It is possible to make a supply with these IC's without external current limiting circuits as long as you quickly remove any overload, but for me, I think a power supply needs to be able to look after itself.Richard.

author: Rerouter
author_rank: Super Contributor
timestamp: February 10, 2012, 11:49:31 pm
content: or if your just looking for a safety envelope type current limit, you can use a thermocouple, or thermister in a divider, and use the voltage output from that trigger a comparitor like in daves supply,being at short circuit, its the heat that will kill the thing, not the the current by itself,(set below the maximum temp of the regulator to compensate for the time it takes to reach the thing your measuring with)as for what to trigger, you could either try pulling the output to a low voltage, however that will increase the wattage on the ic, but with the diode mod, you should be fine,

author: Unknown
author_rank: Unknown
timestamp: February 11, 2012, 12:15:29 am
content: It's not just about not killing the regulator, but also about not melting the bond wires of the ICs in your circuit. An adjustable current limit is the best way to accomplish this. Constant current mode is also occasionally useful, for example for finding shorts. Shove some current through it and measure the voltage drop.

author: sacherjj
author_rank: Frequent Contributor
timestamp: February 11, 2012, 01:50:52 am
content: Quote from: alm on February 11, 2012, 12:15:29 amI never considered that use. It is a logic idea once you consider it though. Nice little trick to add to the bag.I will never use a lab supply without current limit. At least not for the first run of a new circuit design. Doing this would have saved me many parts and burns on fingers ripping wires out.