120VAC Input to 5V/1.25W Output: Ultra Compact Isolated SEPIC

The PMP6711 reference design provides an isolated 5.5V at 250mA from a 120VAC/60Hz input in less than 1 square inch of board space. This design uses the TPS40210 in an isolated SEPIC topology with primary side regulation: eliminating the extra space and cost associated with an opto-coupler feedback. The SEPIC clamping capacitor reduces ringing on the drain of the MOSFET and recaptures leakage energy to improve efficiency.