Power Supply - Page 1
Forum section: electronics / beginners

author: thomst77
author_rank: Contributor
timestamp: June 30, 2013, 03:38:31 am
content: So one of the first projects a beginner tackles is a power Supply. I have been looking around for a kit or recommendations. I have a few ATX Power supplies. And that seems easy enough to do, But I would like a variable voltage option. Maybe 1.25 to around minimum 12 volt DC and maybe 2A minimum. Are there any kits that you all would recommend? Or maybe a simple circuit for an ATX Power supply? I was thinking maybe a voltage regulator circuit on one of the 12v leads? Maybe an lm317t with a beefy heatsink and maybe even a small fan blowing across it? I would appreciate any input. Also I am well aware of the safety issues. I am an Amateur Radio Operator and have put together a few kits in my time.Thank You in advance for your inputTom

author: Rerouter
author_rank: Super Contributor
timestamp: June 30, 2013, 04:02:20 am
content: if your planning 2 amp minimum, you may want to dip your toes into a multi-tap approach or switcher module following the atx on its own, as 2x 10.75V minimum is a big amount of heat being pissed away,as your likely to only be using the regulator stage as an output, you cant make use of the 7V difference between 12V and 5V, as the 5V rail on just about every atx supply can only source and not sink current on the 5V rail, (just incase you try it from fan mods on forums)

author: Alana
author_rank: Frequent Contributor
timestamp: June 30, 2013, 09:16:17 am
content: When i was starting my electronics adventure i wanted a big PSU, variable voltage with several amps of power. I made one and only high current application of this psu was powering a HV generator and playing with arc-welding using carbon electrodes.Later i noticed that all i need is some reliable 5V PSU for micros and TTL logic and +/- 12V or even +/- 5V for analogue stuff. Current consumption rarely exceeded 1A.Regulated PSU - good to have one but most of the times i used this capability it was for testing LEDs without series resistor and for charging battery packs.So:you got your ATX PSU with +5V +12V -12V and if its older device also -5V and this is basically all that you need.If you are into new micros you have +3.3V rail as well.If you are into audio stuff you may add pair of 7805/7905 powered from +/-12V rails to get rid of any noise and ripple. Its worth to do it because -12V rail is poorly regulated and can be anything from -9 to -13V.

author: Rerouter
author_rank: Super Contributor
timestamp: June 30, 2013, 11:15:15 am
content: also worth noting on the ones that have a -12V rail, it can generally only sink a few hundred milliamp at best, and is very easy to disable via overloading for more than a few odd minutes,also be aware most modern ones need a load on the 3.3V rail to keep the other rails in spec,

author: Paul Price
author_rank: Super Contributor
timestamp: June 30, 2013, 11:34:33 am
content: ATX power supplies are great, but without hacking their innards to get the voltage above 16V you'll not be likely to get 12V adj. able output with an additional regulator.My simple solution is to find a discarded 18-21V laptop power supply, most can deliver 3 to 4.5 amps and this is the perfect to launch a switcher like the one below that will give you 1.2V to approx 19V at the capacity of the wall wart.And it so much more compact than the ATX power supply.

author: thomst77
author_rank: Contributor
timestamp: July 01, 2013, 01:18:11 am
content: Quote from: Paul Price on June 30, 2013, 11:34:33 amThanks for the recommendation. I had not thought about this. I think I have one of these somewhere.