I'm working on a dual rail power supply that will provide DC current for 4 power amplifiers.
Two of them require 20V and the other two 25 – 50V. All 4 draw a maximum of 2.5A of current, hence my transformer is 24+24V, 10A. Currently I have the output of the transformer to a rectifier bridge and on each rail 10.000µf capacitors, resulting in 35V.
My question is: how I drop this voltage to 20V, allowing a maximum of 5A of current to flow through? I've read about shunt regulators but it seems I would need a very large resistor and zener for this amount of current.
Are there other options? Which is the most suited for this case?
Best Answer
A switching regulator like John suggests would work in principle, and any experienced electronic engineer would probably find it trivial, but keep in mind that that chip is effectively funneling all of that power through a 4mm square plastic package with no leads and that pretty much all the heatsinking is on the bottom (board side) of the chip. This makes the PCB design a bit tricky in that area for the uninitiated. See section 10 of its datasheet.
A less demanding solution in terms of heat removal would be to separate out some of the functions that that chip does, thus providing more surface area for the heat to dissipate, but it only shifts the PCB difficulties into avoiding parasitic interactions between parts that should not interact.
To keep it simple, I'd be tempted to go with a separate, lower voltage transformer/rectifier/filter for the smaller amps. If you happen to find a transformer that has a single primary and multiple secondaries that collectively meet your requirements, you can make it that much more compact, but those are comparatively rare.