Sub Coverter Unit; The Detection Of The Fan's Rotation Speed - Sony VPL-VW12HT Service Manual

3-1-2-4. Sub Converter Unit
This uses a current resonance type converter using an DC/
AC ferrite transformer.
The resonance circuit consists of T2602 sub converter
transformer and orthogonal transformer T2601 and C2611.
The output from the secondary side of T2602 consists of
sub 5V only, and after full wave rectification by the
rectification circuit consisting of D2602/C2613 this is
output through line filter (L2601/C2615).
The output from the primary side consists of Vcc (19.5V)
only and is output through the rectification circuit of
D2601/C2606.
Stabilization of the output voltage is achieved by detection
of changes in the sub5V voltage by IC2602 and varying of
the oscillation frequency. In reality, this is implemented
by varying the current flowing in the secondary coil of the
orthogonal transformer so as to move the resonance point
(frequency) of the preceding resonance circuit.
IC2603 latches the sub5V output to about 2V by setting the
control current of the secondary coil of the orthogonal
transformer to its maximum value with the sub5V over
voltage protection circuit (OVP).

3-1-2-5. The Detection of the Fan's Rotation Speed

Input the detection pulse of the fan's rotation speed from
CN2008(pin 4). Input the IC5005(pin 28) of C Board
through BM Board. The detection of the fan's rotation
speed is performed when the power is on. The change (of
the fan's rotation speed) is measured when the clogging of
air filter is detected and alarmed.
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VPL-VW12HT