General circuit description

STEVAL-ISA002V1

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General circuit description

This board is designed as a discontinuous flyback regulator delivering 0.5A at 12V. The AC

input is rectified and filtered by the bridge BR1, the bulk capacitor C1, and C2 to generate the

high voltage DC bus applied to the primary winding (pins 8-10) of the transformer, TR1. C1, L1,

and C2 provide EMI filtering for the circuit. R2 and C3 form the snubber circuit needed to

reduce the leakage spike and voltage ringing on the drain pin of VIPer12A. The output voltage

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

ripple is controlled with the capacitor, C7, with an additional LC PI filter configuration made up

of L4 and C8. It is possible to modify the output voltages by changing the transformer turns ratio

and modifying the resistance values of R6 and R7 in the feedback loop.