STEVAL-ISA001V1 Datasheet, PDF (2/5 Pages) STMicroelectronics – 6W Dual Output Supply using VIPer12A

General circuit description
1 General circuit description
STEVAL-ISA001V1
The circuit operates from 85Vac to 264Vac input voltage with an output power peak of 6W
through two output voltages of 5Vdc and 12Vdc. It contains an input fuse (F2), EMI filtering (C1,
L1, and C2), and the secondary regulation is provided by U2 and U3, the optocoupler and
TL431 respectively. For output filtering, the components used are the output capacitors C8 and
C10. These two output capacitors are sized according to the ripple current and ripple voltage
specifications. The two specifications determine the ESR and RMS current capabilities of the
capacitors used. An additional LC (PI) filter is added to the 5Vdc output, C9-L2 configuration,
for further effective ripple and noise rejection. The AC input is rectified and filtered by the bridge
BR1 and the bulk capacitor C1 to generate the high voltage DC bus applied to the primary
winding of the transformer, T1. The 5Vdc output is sensed with an optocoupler. It is possible to
modify the output voltages by changing the transformer turns ratio and modifying the resistance
values of R7 and R8 in the feedback loop. R2 and C4 form the snubber circuit needed to
reduce the voltage ringing on the drain pin and the leakage spikes.
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