NEC DTE-29U1TH Service Manual page 41

Service Manual CP-785F
When the power switch is pushed on, V
through R802.
As soon as V reaches 16V, the STR-F665X control circuit starts operating. Then, VIN is
IN
obtained by 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
IN
before V voltage drops to the shutdown voltage (at 11V), the control circuit continues
IN
operating (see below V
according to the secondary side output current.
V must be set higher than the shutdown voltage (VIN (off) = 11Vmax) and lower than the
IN
O.V.P. (overvoltage protection) operating voltage (V
O.V.P.voltage 20.5V
16V (TYP.)
Shutdown voltage 11V
starts dropping. However, as this winding voltage reaches the set value
voltage at start-up). R805 resistor prevents that V
IN
Vin
Waveform of Vin pin voltage at start-up
increases slowly. During this time, C806 is charged
IN
= 20.5Vmin)
OVP
-40-
pin voltage varies
IN
t