Building my own mini DC power supply (beginner)

[amateur_24]

Hi
I was thinking of building my own power supply because it's a bit of pain having an old pc power supply on my desk. I was thinking the safest / easiest way was to use an normal 12 Volt DC adapter then lower the voltage to 5V and 3.3V. So I get 12V, 5V and 3.3V. I know there are ready built power supplies but it's expensive and I found the simpler ones only have 1 output voltage.

The only difference is in a pc power supply the amperage it can output pair line is higher but for general electronics one ampere should be fine right?

Also the more expensive power supplies have all these protection features:

Under voltage protection
over voltage protection
over current protection
Short circuit protection

I'm guessing a voltgage regulator would do all this for me right?
Because I have 3 separate voltages, I need 3 channels right?

 

[MikeMl]

If you need 12VDC that is well-regulated, you will need to start with a Wall-Wart that is regulated (most are not), or you will have to start with one that puts out a higher voltage (like 15V to 18V), and then use a 12V regulator chip. Getting 5V and 3.3V off the 12V at any substantial output current will produce a lot of heat dissipation, so you will have to consider the heatsinking requirements for the regulators carefully.

 

[ronv]

You might consider an LM317 regulator. They are almost bullet proof and easy to make adjustable for the ranges you are talking about. If you live in the US, Radio Shack has about the cheapest 12.6 volt transformers around that are good for an amp or 2. You can pick up a 20 volt voltmeter for 5-6$ and a good sized heatsink and be on your way!
Good Luck!

 

[amateur_24]

yeah but I don't have any experience with transformers/ high voltage so I better not go there. In the uk it's 240 volts not 115volts!!.
The power adapter which would be the same thing but built by a professional.

 

[ronv]

Ouch! Bet that does make you smoken mad when you get across it. That would make the adapter a good choice!

 

[zipdogso]

Why is it a pain having an old PC PSU on your desk ?

If you mean it doesn't look great or you dont like all the wires why not just box it up ?

If you only want 12v, 5v and 3.3v why go to the hassle of building something the PC PSU already does ?
With all the protection circuits modern ones have they are very safe in operation.

There are loads of instructions on the net on how to do it.

Google - "convert psu to bench supply"
How far you want to go with the tidying up is up to you.

I had a load of stuff laying about so I just used it.... so it is a bit over done. If I had to buy the stuff I wouldn't of bothered it would be too expensive for a simple project like this.

**broken link removed**

**broken link removed**

Instead of using the GND use one of the others as the GND you can get other voltages.
My particular PSU can supply 1A on the -5v and -12v. So if you only want 1A or less you can get quite a range of voltages. -12v as the GND and 12v gets 24v at 1A max.