Variable power supply questions - Page 1
Forum section: electronics / general

author: jollyOne
author_rank: Newbie
timestamp: October 04, 2014, 10:46:54 pm
content: i found this in Elektor #092 - December 1982 0v - 35v at 3 amp's but it seems a little dated i was wondering if anyone could point me to a good open source schematic that is a little more up to date, or ideas for bringing this one into the modern world?

author: steve30
author_rank: Frequent Contributor
timestamp: October 06, 2014, 12:55:18 am
content: Hi jollyOne. I'm not an expert, but I had a glance over that circuit, and it seems quite simple, and uses bog standard easy to get components (741 and 723).The 723 regulator could probably be replaced with a more modern part, which would have better stability etc, and be easier to use. There are many good ones, both old and new. The old fashioned LM317 is pretty good, and the more modern (but expensive) LT3080 seems quite popular on these forums.Not sure what to suggest with regards to the op amps used. There are op-amps which are much better than the 741, but it is still a perfectly usable part provided you can design around its limitations (which they probably did given that the schematic is very old).Have you designed/built any power supplies before?

author: jollyOne
author_rank: Newbie
timestamp: October 06, 2014, 05:45:02 am
content: no i haven't this is my first attempt at it i have it pretty close to done breadboarding but i want to make it as good as possible if you know what i mean if you have a better recommendation on how to go about it im all ears ^_^ thank you for your help and advice

author: steve30
author_rank: Frequent Contributor
timestamp: October 06, 2014, 12:27:44 pm
content: If you have it breadboarded, you might as well finish it off and see how well it works. Once you have it working, you can always look at improving it then.Let us know how you get on.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: October 06, 2014, 12:29:17 pm
content: looks good to me,most of the important stuff has been well considered ( reverse polarity protection diode missing though). Remote sense included which is a nice feature.Looks effective n cheap ,the designer's got the loops really tight ( only 47uF on the output)which is good.You could replace the 723 V reg with somthing more 'off the shelf' if you wanted . the 741's probably could be repaced by one of the many drop in replacement (perhaps like the TL071),but doubt it would make any significant improvment over 741's .A few cheap changes would be to replace the analogue meters with a digital panel meter's .Also I would add the ability to dissable/enable the output and also preset the current limit when output is dissabled (without shorting the output),both these can easily be added here with a few components.Regards

author: jollyOne
author_rank: Newbie
timestamp: October 06, 2014, 05:40:25 pm
content: i have been doing a little research on switches for disable/enable the output but i have been confused a little on what type of switch to use for it i know some of them can have massive spikes and noise when you flip them is there a specific one you would recommend to eliminate this issue?

author: calexanian
author_rank: Super Contributor
timestamp: October 06, 2014, 06:29:17 pm
content: Still a very practical circuit. There are switching circuits that have replaced this sort of linear circuit. For something in the same ballpark, but a little less in voltage and power handling I real world use, I would look at LM2596 based circuits. Its a very forgiving device and little module boards are available on line for peanuts.

author: Kevin.D
author_rank: Frequent Contributor
timestamp: October 06, 2014, 10:15:29 pm
content: Quote from: jollyOne on October 06, 2014, 05:40:25 pmWell normally you would use electronic switches like transistors where you want fast switching with no bounce .But you can use real switches here if you want since speed is not important ,you just have to 'debounce' them using a capacitor and resistor. You dont need a high current switch ,since you can dissable output by switching off drive to pass trans. To keep it easy here just try something simple like this .Use a dpdt switch so you can simulataneosly switch the ammeter so it display's the 'I set' pot output when output dissabled so you can preset it , and then displays true current output when output enabled .Capacitor C1 I added here should of already been here by rites (pots can be very noisy and always need decoupling) ,this cap will debounce the enable switch and will also ramp up the output slowly when you enable the output (ramp up set by C1 *R13 ),ramp down (dissable time so it's not really critical) should take about 1 sec with 1 uF and a 741 ( C1 will disscharge into 741 input at about a rate 500nA input bias) ,so you shouldn't need R99 unless you replace 741 with another opamp .Good luckP.s :- Just realized you won't of course be able to 'preset' the voltage when your in disabled output since your V meter is still connected to output so will show 0,hence you can still only preset V with output's enabled . If you wanted also to preset that ain diss then you would have to also switch the V meter over to display the V cntrl pot output .(easy in a digital cntrled supply but in an analogue cntrl supply it's a bittrickier because youd have to take into account of the ratio r4/p1 in your V meter.

author: jollyOne
author_rank: Newbie
timestamp: October 07, 2014, 06:53:19 pm
content: thank you for the help i will keep updates posted