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When the power switch is pushed on, V
R802.
As soon as V
reaches 16V, the STR-F6654 control circuit starts operating. Then, V
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
IN
voltage drops to the shutdown voltage (at 11V), the control circuit continues operating (see below V
voltage at start-up). R805 resistor prevents that V
output current.
V
must be set higher than the shutdown voltage (V
IN
(overvoltage protection) operating voltage
(V
= 20.5V
)
OVP
min
Vin
O.V.P.voltage 20.5V
16V (TYP.)
Shutdown voltage 11V
increases slowly. During this time, C806 is charged through
IN
pin voltage varies according to the secondary side
IN
Waveform of Vin pin voltage at start-up
- 40 -
Service manual CP-785A
(off) = 11V
) and lower than the O.V.P.
IN
max
is obtained by
IN
IN
IN
t
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