Symmetric power supply

[Tafie]

Hi everyone! I need to build a symmetric 12V(±12V) power supply using discrete components. I need a simple functional transistor circuit.

 

[duffy]

If it's less than an amp, I suggest just using a LM7812 and LM7912. Quick and easy, works great, thermal protection, one part and a couple of caps - done.

 

[Tafie]

Symmetric PS

The thing is I only have a 20V transformer, diodes, 7812 and a bunch of transistors and other basic discrete components. I dont have 7912. I was hoping that its possible make a transistor circuit.

 

[Hero999]

Does the transformer have two windings?

What's its maximum current rating?

I would suggest buying an LM7912, they're not expensive.

 

[duffy]

Yeah, you're going to need two windings. If it's center-tapped it might do it if the rectified, filtered voltage comes out over 12v each side - but even then you are probably going to need low-dropout regulators (the 7812 needs a 3v differential).

 

[Tafie]

The transformer has a single winding and about the current rating im not too sure if there is a way of testing to find out since there is no inscription on it. I'll consider the 7912 option.

 

[duffy]

The 7912 is no longer an option. You should have taken it when you had the opportunity. Now you must quest to seek the Transformer of Two Windings.

 

[ericgibbs]

The transformer has a single winding and about the current rating im not too sure if there is a way of testing to find out since there is no inscription on it. I'll consider the 7912 option.

You could use a second transformer for the 7912 or buy a 12Vdc wall wart psu.

Where are you located.?

 

[bassnut]

Unwind half the secondary, tap it off, and rewind, giving you the opportunity to use the 7912 option ;-). Or purchase another transformer, cheapskate ;-).

 

[eblc1388]

Half the turns of a 20V transformer is 10V.

The transformer will then not work for both the 7812 and the 7912.

 

[ericgibbs]

The transformer has a single winding and about the current rating im not too sure if there is a way of testing to find out since there is no inscription on it. I'll consider the 7912 option.

You could do it this way, not very elegant, but its +/-12Vdc

 

[Hero999]

That will certainly work but if significantly more current is drawn from one rail than the other then the transformer's core might saturate and overheat.

 

[duffy]

Yeah and it's half-wave, but it IS a solution.

 

[Hero999]

It depends on what it's being used to power, if it's a general purpose bench-top PSU then I wouldn't recommend it but if it's being used to power an audio amplifier it's ideal as the current draw is roughly symmetrical.

 

[Nigel Goodwin]

It depends on what it's being used to power, if it's a general purpose bench-top PSU then I wouldn't recommend it but if it's being used to power an audio amplifier it's ideal as the current draw is roughly symmetrical.

HUMMMMMMMMMMMMMMMMMMMMMMMMMMMM!!!!!!!!!!!!!!

 

[MrDEB]

A rail spliter circuit = virtual ground

If you want a virtual ground PS the perhaps the attached pic will help?

 

[ericgibbs]

hi hero,
The definition of STEREO sound comes to mind, also the current drawn from the +V and -V rails will not be symmetrical.