SIMPLE power supply - Page 1
Forum section: electronics / projects

author: ICSB_Tech
author_rank: Newbie
timestamp: April 01, 2012, 08:51:27 pm
content: All this talk about power supplies and such have inspired me to go get/make one myself. I've been looking around for a simpler design but I'm not really sure what to look for. Usually I work with audio stuff, mostly effects pedals (usually 9V) and microcontrollers.Maybe you'd have some advice for a simple linear power supply, here's the specs I'm looking forVoltage up to 9v (maybe 12V, but that's not completely necessary)Doesn't need to be highly adjustable, just like have a 3.3V, 5V, and 9V settingsmaybe current limiting? (I'm not really sure how to do this part, I understand the voltage, but not sure how to limit current)Powered by a wall wort, 9V or so (I live in Europe, and I'm moving back to America in a few months, so I don't want something with a transformer)Advice on what parts to use, or maybe even a schematic would be awesome!

author: cyberfish
author_rank: Regular Contributor
timestamp: April 02, 2012, 03:24:54 am
content: Adjustable current limiting would be the hard part.Otherwise you can just use a LM7809, LM7805, and a 3.3V linear reg.It also depends on what kind of current you need.

author: TriodeTiger
author_rank: Regular Contributor
timestamp: April 02, 2012, 04:21:40 am
content: Something like twoLM317's would look like something you can do. It's a common item in DIY power supplies.Voltage adjustment:You can replace the voltage pot (R2 in next figure, which works as in a voltage divider configuration) with a selector switch and appropriate resistor values for 3V3/5V/... if you do not wish for more adjustable voltages.The formula means more or less "Vout = Vadj + Vref", meaning the range will be from 1.25V (Vref) to (Vin-Vdrop). You should get up to near 10V out on a 12V plugpack. If you want 0V, you can offset with -1.25V, although with added complexity.Current limiting:The current pot (R1 in next figure) can be replaced with a power resistor to keep the limit to say 500mA. Resistor must be able to dissipate I^2*R watts as it is in series with the load. Current limiter will drop some voltage, so it should go before voltage reg. You may get 1.25->9V with it added, however that is fairly good for its simplicity.LM317 can go up to 1.5A if I recall with heatsinking. LM350 to 3A. Not sure what your current requirements were.http://www.digikey.ca/product-detail/en/LM317T/LM317TFS-ND/458678@ $0.71 each

author: BravoV
author_rank: Super Contributor
timestamp: April 02, 2012, 04:25:24 am
content: If you want simple regulator yet have current limiter, look for L200 ic.

author: TriodeTiger
author_rank: Regular Contributor
timestamp: April 02, 2012, 05:14:52 am
content: Quote from: BravoV on April 02, 2012, 04:25:24 amNot a bad part! I'd say the 2.85V minimum voltage output is a little high, but fine for the 3V3 he asked. It's only $2 too.

author: BravoV
author_rank: Super Contributor
timestamp: April 02, 2012, 05:31:28 am
content: Quote from: Alexander on April 02, 2012, 05:14:52 amExactly, quite cheap, pretty easy to build and almost indestructible and fool proof even used by a noob.

author: Jeff1946
author_rank: Regular Contributor
timestamp: April 03, 2012, 12:13:07 am
content: Agree with others, you might use power supply from an old laptop as a DC voltage source to power the regulators discussed by others. Most will work on 100-240 volts. Hopefully you can get one for free from someone with a dead laptop.

author: Monkeh
author_rank: Super Contributor
timestamp: April 03, 2012, 02:29:59 am
content: Quote from: Jeff1946 on April 03, 2012, 12:13:07 amIndeed, that's going to be the basis of a supply I'm putting together shortly. It's often easy to find them with damaged cables or connectors which you can repair or replace easily, I have one with the connector falling off.

author: saturation
author_rank: Super Contributor
timestamp: April 03, 2012, 12:53:42 pm
content: As there are many well known approaches to a making a simple stable linear supply, for decades they have sold these as kits. It will save you a lot of time and energy, just check Amazon.com or others. The key is understanding how the parts are used as you assemble them:http://www.amazon.com/Velleman-1-5V-35V-Power-Supply-Kit/dp/B0002Z82PS/ref=sr_1_1?ie=UTF8&qid=1333457301&sr=8-1http://www.amazon.com/Elenco-0-15V-Power-Supply-Kit/dp/B0002DVF4K/ref=sr_1_1?ie=UTF8&qid=1333457271&sr=8-1

author: sorin
author_rank: Frequent Contributor
timestamp: April 03, 2012, 10:16:12 pm
content: https://www.eevblog.com/forum/projects-designs-and-technical-stuff/general-purpose-power-supply-design-7488/

author: T4P
author_rank: Super Contributor
timestamp: April 03, 2012, 10:45:21 pm
content: A simple power supply consists of a 7805 with a 10C/W heatsink off a 6VAC tap (rectified 7.1V)7812 with a 10C/W heatsink off a 12VAC tap (rectified 14.9V)For higher currentsOr you can simply use the LM323 or the LM2576And you can also use LM723 switching a transistor to get 0-37V instead of the LM317http://www.bristolwatch.com/ele/lm317.htmBut really if you don't want to spend much money on heatsinks , get switching ones if you want high current capability .