Daewoo DTA-14C4TFF Service Manual page 29

8. Power supply (STR F6653)
8-1. STR-F6653 general description
The STR-F6653 is an hybrid IC with a build-in MOSFET and control IC, designed for flyback converter type switch mode power
supply applications.
8-2. Power supply primary part operations
An oscillator generates pulse signals which turn on and off a MOSFET transistor.
8-2-1. Start -up circuit: V
The start-up circuit is used to start and stop the operation of the control IC, by detecting a voltage appearing at the V
Main AC voltage
When the power switch is pushed on, V
As soon as V reaches 16V, the STR-F6653 control circuit starts operating. Then, V
IN
age which appears between pin 6 and pin 7 of the SMPS transformer.
As this winding voltage does not increase to the set voltage immediately after the control circuit starts operating, V
ping. However, as this winding voltage reaches the set value before V
trol circuit continues operating (see below, V
some regulation of the SMPS transformer occurs due to secondary side output current
V must be set higher than the shutdown voltage (V
IN
ing voltage (V = 20.5V
OVP
IN
D804
D801 C804
C803
R819
D802 D803
R802
increases slowly. During this time, C806 is charged through R802.
IN
voltage at start-up). Resistor R805 prevents variations of voltage at the V
IN
).
min
2
C805
C806
Ground
voltage drops to the shutdown voltage (at 11V), the con-
IN
(off) = 11V ) and lower than the O.V.P. (overvoltage protection) operat-
IN max
7
FUNCTIONAL DESCRIPTION
T801 SMPS TRANS
4 6 7
R805
D805
L801
3 4
Drain Vin
I801 STR-F6653
5
is obtained by smoothing the winding volt-
IN
APPENDIX
pin (pin 4).
IN
starts drop-
IN
pin, as
IN