STEVAL-ISA002V1 Datasheet, PDF (2/5 Pages) STMicroelectronics – Switching Frequency 60 kHz

General circuit description
1 General circuit description
STEVAL-ISA002V1
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.
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