I need a circuit that converts a 2-phase, 26 vAC, 400 Hz input to +/- 15 vDC (may get away with +/- 12 vDC). Only need about 125 mA for power.
I have very little board real estate to work within. Can I do this with a 4-diode full wave rectifier and some voltage regulation, thereby skipping the need for a transformer?
Is the 2-phase AC input versus a single phase going to complicate things?

Thanks.

 

By 2 phase you mean a neutral wire and two live wires?

 

Yes, that's correct. Two live and one neutral.
Thanks.

 

You'll lose 1v across the rectifier bridge, and more across the regulators.

What is the board space that you have to work with?

 

Use one phase and neutral to produce the positive supply and the other phase and neutral to produce the negative supply.
You can use a bridge rectifier for each of the voltages you want. However, a half wave rectifier might work because you need only 125mA if you use a large filter capacitor and if the AC source can provide enough current to charge the capacitor quickly.

 

Sorry I closed this thread - I saw 400 Hz and assumed 120 VAC.

As the lady on SNL used to say, "Never mind".

 

Sorry I closed this thread - I saw 400 Hz and assumed 120 VAC.

As the lady on SNL used to say, "Never mind".

Emily Litella, played by Gilda Radner

http://en.wikipedia.org/wiki/Emily_Litella

 

I have approx. 1.0 x 1.25 inches. Not much room.

Thanks for the response.

Semper Fi, brother.

 

Thanks mik3. I'll see if I have the board space for a bridge rectifier, otherwies I'll give the half wave a shot.

 

Have a look at the attached. I've used a simple configuration that won't protect against shorts or overheating, but has a much lower dropout than an LM317M or 78Mxx/79Mxx series regulators, and as the parts are available in TO92 cases, are reasonably small. You could opt for SMD/SMT equivalents as well. Regulation won't be as good as the aforementioned regulators, but it should be reasonably stable within a few mV's, depending upon the nature of your load.

Your big problem (literally) is finding suitable capacitors that have a small enough footprint.

The diodes are no big deal (sic); you can position them all vertically.

I'm afraid you're not going to make it with a halfwave rectifier scheme; you'd need to use much larger capacitors. Their increased footprint will send you back to the drawing board.