I need to build and design a dual ouptput PSU +/-5v and +/-12v.?

Question

Hi There. I need to build and design a dual ouptput PSU +/-5v and +/-12v. I understand the different stages necessary and possible arrangments of components(I Think) What I dont understand is how to get the two output supplies in one circuit.

I originally thought I needed to use a centre tapped transformer, but from further reading I realised I can get +/- voltages but only for one voltage. ie 5v or 12v but not both simultaneously. Is this right or am I mis-understanding it? Hope you can help.

Answer 1

If you want a proper dual O/P PSU, you will need two O/P's from the transformer. You could of course just generate +/_ 12v and tap down to get your 5v, but you might get loading problems.

Answer 2

Hi

Assuming that you mean a linear supply as opposed to switch mode suppply.

You can use a centre tapped transformer if you want to, or if you have one handy!

The centre tap becomes the common ground.  The two ends connect to a Bridge rectifier.  The two anodes from the diodes within the rectifier become +ve, the two cathodes become the -Ve supply.

If you have a high enough initial secondary winding on the transformer, you can indeed run a variety of voltages, both +VE and -VE.

ie if your transformer has a secondary output of 15-0-15 then there is no reason why you cant put a voltage regulator (ie 7805 - +5v, 7905 -5V) to produce a variety of outputs.  Oh yeah - dont forget the smoothing capacitors and chokes.

Email me for a more concise description and schematic if you need to.

Answer 3

Make sure it puts out over 12 volts of filtered DC and simply use transistor voltage regulators on the output. There are a great variety of these depending on your current needs. Easy to wire and relatively cheap!

Answer 4

Unless you are doing this for education or you need fairly large currents on your negative supplies, don't bother. Rob one from an old PC.

I use one to power up a car radio in my shed and the outputs on that are



25A at +5V

10A at +12V

0.5A at -5V

0.8A at -12V

Admittedly the -5 and -12V rails don't have much oomph but they are enough for experimenting.