28Vac to 5 x 12Vdc @3 to 5A PS

[DrWhoF]

I need a power supply which will convert 28Vac (aircraft power) to 5 outlets capable of powering loads at 12Vdc and currents of 3-5A.
Any ideas?
This power supply has to be mounted in a metal enclosure and should have all safety features such as fused inputs and outputs, overvoltage and current limits.

Thanks.
DrWho

 

[IanP]

28Vac x 1.4 ≈ 39.2V dc This ius how high will be the voltage after rectification ..

If you can work with 3.5A then I would go for LM2576HVT-12 (or ADJ) as only these switching regulators are rated for input dc voltage >50Vdc, and, I think, you need that margin ..

So, select bridge rectifier, say, 25A-35A ( http://www.futurlec.com/DiodesBridge.shtml ) and use 1000µF capacitor per 1A output, of course rated for at least 50Vdc, I would go for 63Vdc ..

And build 5 identical channels fed from the same 39.2V dc based on the LM2576HVT switching regulators: **broken link removed**

As the LM2576 has internal current limit the only output protection that I think of will be a fused >12V crowbar .. below is an example of one such circuit ..
This circuit can be simplified by replacing comparator and it's associated components with a 12V zener diode connected between the output and 1kΩ resistor (SCR's gate) ..

Regards,
IanP