SEPIC (5V@250mA) for Auxiliary Bias Supply

The PMP5298 reference design provides an isolated 5V at 250mA from a 120VAC/60Hz input in less than 1 square inch of board space. This design uses the UCC3813-5 in a non-isolated SEPIC topology. The SEPIC clamping capacitor reduces ringing on the drain of the MOSFET and recaptures leakage energy to improve efficiency.