Bench top power supply - Page 1
Forum section: electronics / beginners

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 01:23:46 am
content: Excuse my poor articulation of words this is my first post on the forum.As I've started making projects I've decided that I need a power supply.My problem is that I've got a very small budget (around $50 aud) and was thinking if anyone had a way to get a cheap power supply or maybe even make one myself.Would anyone have a simple schematic?Thanks

author: Rerouter
author_rank: Super Contributor
timestamp: April 05, 2014, 01:32:07 am
content: You never said what voltage or current range you need,For the cheapest you could get away with, find an old ATX power supply, and you have moderate current 3.3, 5 and 12V, (dont try using the -12 or -5 rails on older supplies there only good for a few mA at best)if you want more control than that, then grab a transformer (remembering the rectified voltage will be about 1.4 times the AC voltage of the transformer) and make up a lm317 (or lm317/lm337 on a center tapped transformer for split rails) supply, remembering every volt not used has to be burned up as heat,

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 01:41:20 am
content: Quote from: Rerouter on April 05, 2014, 01:32:07 amThanks,I think I'll need no more than 12V most of the time with around 1-3A.I might try a transformer since I'll need 9v most commonly and an ATX power supply cannot output 9v and a battery won't provide enough current.

author: han
author_rank: Frequent Contributor
timestamp: April 05, 2014, 01:46:16 am
content: I build switching adjustable 0-3A , 0-12V, and power it using Laptop power supply.it only cost about <$20 to build.If you interesting i will upload the schematic and photo..

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 01:48:46 am
content: Quote from: han on April 05, 2014, 01:46:16 amYes please,That sounds like exactly what I need

author: han
author_rank: Frequent Contributor
timestamp: April 05, 2014, 03:03:50 am
content: definitely ,not the world best P/S... But it's workHere the pic and "handcrafted" schematic,sorry for the crude drawing.I build it a long time ago, so have to open and make new schematic..

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 03:18:34 am
content: Quote from: han on April 05, 2014, 03:03:50 amThank you very much, this is perfect for my use

author: Shock
author_rank: Super Contributor
timestamp: April 05, 2014, 07:09:58 am
content: Looks really cool, but oh man that fuse holder did you have to? hehehe I would have sprung for a buck on that one and gone panel mount.

author: han
author_rank: Frequent Contributor
timestamp: April 05, 2014, 07:56:04 am
content: The fuse is from my old motorcycle.. Which i didn't have anymoreI didn't buy anything for that (only buy banana jack/plug)..all is University project leftover even the used protoboard PCB..<$20 is the cost of brand new component..but in my case, the P/S cost <$1

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 09:38:03 am
content: I've noticed in your photo that you have 4 trimpots but in your schematic you have only one.which resistors are trimpots or are they just a replacement for fixed value resistors.

author: han
author_rank: Frequent Contributor
timestamp: April 05, 2014, 10:09:39 am
content: Actually i use 3,The 4th is not used since i use LM2576-5 (the FB is connected to 5V directly)

author: electron_misfire
author_rank: Contributor
timestamp: April 05, 2014, 10:19:51 am
content: Oh, wow I must be really stupid to have missed those. Also are the diodes for the feedback area on the bottom left 1N5822's too?

author: han
author_rank: Frequent Contributor
timestamp: April 05, 2014, 10:25:49 am
content: the diode is for reducing voltage from Opamp pullup resistor, use regular diode (1n4148 or 1n400x (x is the voltage rating anyting will do))- first trim pot from the left is for compensating voltage drop when the P/S is loaded- Second one is for set the maximum output for I and V of the P/S- Third one is for calibrating/Set voltage feed back and Voltage readoutnote: the schematic is not the best one, open for improvement, like:- Adding LC filter to output- more smaller filtering capacitor (on input and output)- Use 12 bit DAC digital control.(MCP4922)