Creating a variable power supply - Page 1
Forum section: electronics / beginners

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: May 21, 2013, 04:34:42 pm
content: Hello everyoneHow would i go about designing a constant voltage and constant current power supply?I need it to supply 0-12V (but if it can go higher thats even better) and it need to be able to supply a current of 0-5A.This is just the basics of the cuirchit but it would also be help full if it had a screen showing the current voltage and current but its not nessasary.Another addition to this would be a stability light so i know if the voltage is not correct or if it is drawing too much currentHow would i go about doing all of this?

author: madshaman
author_rank: Frequent Contributor
timestamp: May 21, 2013, 04:43:38 pm
content: Learn about these things:Electronics basicsPotential dividersRectifiersOpamps feedbackControl loopsMosfets/BJTs (series pass elements)Voltage references

author: carbon dude oxide
author_rank: Frequent Contributor
timestamp: May 21, 2013, 05:08:12 pm
content: Thank you very much, i shall start going threw the listis there anything else i need to know for this?

author: KJDS
author_rank: Super Contributor
timestamp: May 21, 2013, 08:28:53 pm
content: Transformersheat dissipation

author: quantumvolt
author_rank: Frequent Contributor
timestamp: May 21, 2013, 09:42:04 pm
content: Do not start studying components as suggested over. You can spend your whole lifetime doing that without ever touching upon your needs. And the box hat you want to make is not a heap of components. It is an application of a DC amplifier with negative feedback - which is a theme in cybernetics and electronic circuit theory.You should imo search the web for 'power supply tutorial'. You will get thousands of pages spot on your needs. If you spend a week studying this topic like you did high school math, you will match or surpass the level of most members on this forum.To make it more fun and less lonely to start, watch this:Then follow YT's suggested videos and do searches on YT yourself. And from there you go to more theoretic tutorials on the web.When you are ready to build, you should search "variable bench DC power supply with current limit". Find 10 real world schematics and identify similarities and differences. Then you can choose and build.You will be our next guru

author: digsys
author_rank: Unknown
timestamp: May 21, 2013, 10:22:47 pm
content: I'm with quantumvolt. Just learn the basic formulas though, so you'll know WHY you burnt yourself on that load resistor :-)For metering, start with a Voltmeter across the output and a current meter in series with the +ve output. Simple and effective.There's also many circuits in these forums, do a search. PLUS heaps of YT videos (as mentioned), especially from Dave.Go for it.

author: Strada916
author_rank: Frequent Contributor
timestamp: May 22, 2013, 10:43:00 am
content: My best advise to you it to buy the followinghttp://www.altronics.com.au/index.asp?area=item&id=K3218and then build it up. Not only will it be fun to make but you will learn along the way. To build a power supply with 5A rating is a little difficult for the beginner to start off on. You may think about modifying the kit to output more power. However it all comes down to the transformer and what it is capable of.

author: rolycat
author_rank: Super Contributor
timestamp: May 22, 2013, 11:06:25 am
content: A design which fulfills the original poster's requirements pretty well can be found here:http://www.eeweb.com/blog/extreme_circuits/fully-adjustable-power-supplyThis offers 0-15V output at up to 5A with variable current limiting and a limit LED.Shouldn't be too hard to add a display of voltage and current if required.

author: Strada916
author_rank: Frequent Contributor
timestamp: May 22, 2013, 03:37:28 pm
content: Quote from: rolycat on May 22, 2013, 11:06:25 amMy only concern about this circuit, is what happens when the power is switched off or on with a load. What usually happens is the negative voltage may disappear before the regulator voltage is dissipated. Which will cause the op amp to drive the regulator hard and blow the regulator. I guess the 1000uF on the negative supply is there to stop that. A way round this is to turn the input voltage on/off the regulator once the negative voltage has gone or present. You can do this with a NPN and PNP transistors and some biasing resistors. I'll post a circuit soon.

author: RPBCACUEAIIBH
author_rank: Contributor
timestamp: May 23, 2013, 01:46:40 am
content: You need an ATX power supply (from a pc) or a laptop adapter, 2 cheep multimeter(for displaying V and A) and some basic skills to build the circuit from the first post:https://www.eevblog.com/forum/beginners/help-understanding-reason-for-ic-placement-on-schematic/that is a 0.8 A max 14V schematic but probably won't give you 0.8A because I don't think ATX is powerfull enough at the -12 out, but with a laptop adapter it should give you 0.8AYou put everything in a box, you connect the -12 and +12 V to the circuit's input, and connect the multimeters to measure the output V and A... That's the easiest way of doing what you need, it's not efficient granted, but easy if you're a beginner, and will give you what you need.I'm about to make that too, but with batteries instead of an adapter.

author: ivan747
author_rank: Super Contributor
timestamp: May 23, 2013, 02:46:08 am
content: Just be careful when using a high current voltage source (like a PC power supply or a car battery). It can supply tens of amps, and that can get some bad explosions when you do something wrong.

author: LloydAZ
author_rank: Newbie
timestamp: May 23, 2013, 02:59:11 am
content: Here's an inexpensive kit that may fit your need.https://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_20626_-1

author: ivan747
author_rank: Super Contributor
timestamp: May 23, 2013, 03:03:21 am
content: I don't like that kit for the simple fact that it has 2 separate potentiometers for the positive and negative voltages, so no track option (using tracking, the voltage in the negative terminal is the same as the positive one, but inverted, of course). And the potentiometers are trimmers, so they will fail soon.You can buy it, but after you build it, find a good enclosure for it and some panel meters as well.Aaaaand 1000th post!