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Service Manual CP-785A
When the power switch is pushed on, V
increases slowly. During this time, C806 is charged through
IN
R802.
As soon as V
reaches 16V, the STR-F6654 control circuit starts operating. Then, VIN is obtained by
IN
smoothing the winding voltage which appears between pin6 and pin7 of the SMPS transformer.
As this winding voltage does not increase to the set voltage immediately after the control circuit starts
operating, V
starts dropping. However, as this winding voltage reaches the set value before V
voltage
IN
IN
drops to the shutdown voltage (at 11V), the control circuit continues operating (see below V
voltage at
IN
start-up). R805 resistor prevents that V
pin voltage varies according to the secondary side output
IN
current.
V
must be set higher than the shutdown voltage (VIN (off) = 11Vmax) and lower than the O.V.P.
IN
(overvoltage protection) operating voltage
(V
= 20.5Vmin)
OVP
Vin
O.V.P.voltage 20.5V
16V (TYP.)
Shutdown voltage 11V
t
Waveform of Vin pin voltage at start-up
-40-
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