General circuit description

AN2063

4/15

DocID10955 Rev 2

2

General circuit description

This board is a flyback regulator, delivering 0.8 A to 5 V. The AC input is rectified and filtered

by the diodes D1, D2, D3, D4, the bulk capacitor C1, and C2 to generate the high voltage

DC bus applied to the primary winding of the transformer, TR1. C1, L1, and C2 provide EMI

filtering for the circuit. D9 and D10 form the snubber circuit, which reduces the leakage

spike and voltage ringing on the drain pin of the VIPer12A-E.

The output voltage is regulated by a TL431 (U3) via an optocoupler (U2) to the feedback

pin. The output voltage ripple is controlled by the capacitor, C7, with an additional LC PI filter

configuration made up of L2 and C8. The output voltages can be modified by changing the

transformer turn ratio and modifying the R6 and R7 resistance values in the feedback loop.