Sony HS75 Service Manual page 35

HS75 Sony
Commute and filter output circuit:
When D Pin of IC901 has pulse output, which makes T901
work, while being given a low level, and there is a current in the primary coil of T901 with a voltage up
terminal positive and down negative, so the secondary coil produces a reverse electromotive force. It is the
stage of storing energy in the coil because D902, D904 are closed. But while being given a high level, The
primary coil produces a EMF with its down terminal positive and up negative, and the secondary coil
appears a reverse EMF at the same time, then D902, D904 get through accompanied with a voltage output
of 12V and 5V through C904, C909 which are used to filter. R901, C918 contained in the RC circuit is used
to absorb the surge voltage produced by D902, while R909, C907 is use to absorb the surge voltage
produced by D904.
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