I am currently designing a 500 watt +-45 V, 5 amp adjustable power supply for an amplifier. Although I have built linear supplies around the same power before, I wanted try my hand at a switching supply. Most of the circuits seen online use some form of flyback converter with a high frequency transformer. I thought for simplicity, I would rectify the AC mains and then use direct PWM to lower the output to 90V+. I would then create a 45V+ source and use it as a floating ground reference to achieve dual rail +-45V output. I understand that my circuit would lack any mains isolation but with voltage of 90V, is isolation completely necessary? I plan to enclose the supply and the amplifier in a properly grounded and protected metal enclosure. Of course I plan on adding over-voltage and PWM switch failure protection to the circuit.

 

The safety point about isolated power supplies is not about you being connected to your own power supply. It is about you being connected to the floor, which is connected to Neutral of the power grid. That makes all your un-isolated supplies capable of shocking you through your feet or elbow, depending on what you are touching.

 

If you have never built SMPS before building a split 90 volt one that can do 500 watts is way beyond your abilities.

Personally, given the low cost of mass produced ones I would just buy a pair of 48 volt 250+ watt ones and use them for the two rials. They would be far more reliable and cheaper than any homebrew design.