If you want a power supply to operate with: Vin = 90 to 265 VAC Vout = 110 or 125 VD Pout = 75 Watts This would be a difficult design but I believe it can be done using a TOP250. Please download our free design software. I would recommend using PIXEls for this design. I have some concerns that need to be addressed. They are: You will dissipate over a Watt of power running your opto circuit off of the main output. You will need to keep this in mind when designing your feedback sense circuit. You could bias the opto with a low voltage output. This would save some power. You will need to add a circuit to provide some feedback signal as the output capacitors are charging during start up. This is needed to get the power supply up and running before the Top Switch open loop protection circuit turns off the power supply at start up. This can be addressed with a soft finish circuit. You will need a 600 Volt output rectifier. These diodes have a long recovery time. Therefore, you will need to operate the power supply in discontinuous mode (set Kp = 1.2) and operate the TOP Switch at 66 kHz (half frequency). Make sure that the rectifier diode has enough time to recover before the next switch cycle. You can reduce the voltage stress on the TOPSwitch by reducing VOR to 100 Volts. It looks like an EF32 transformer core will work or a core of similar size. You will need about 90 turns on the secondary winding. Once these issues are addressed, the rest of the design will be routine. Z. Cochrane

Tks Cochrane. I noted yr info. I will make a protopipe and return with news. byby Antonio