Samsung SV-DVD50 Service Manual page 106

Circuit Operating Descriptions
(d) Feedback Control Circuit
IC1SS2
GND
*
$ % #
DRAIN
&
@
F/B
VCC
1st GND
1) F/B terminal of IC1SF01 determines output duty cycle.
2) C-E(Collector-Emitter) of IC1SF01 and F/B potential of IC1SF01 are same.
◆ Operation descriptions
1) Internal OP-Amp '+' base potential of IC1S03 is 2.5V and external "-" input potential is connected with
R1SS35 and R1SS34 to maintain Vout of 5.8V. (Vout = (((R1SS34)xR1SS35 ) / R1SS35) x 2.5V)
2) If load of 5.8 V terminal increases(or AC input voltage decreases) and Vout decreases below 5.8V, then :
IC1S03 "P" potential down below 2.5V --> IC1S03 A-K of base current down --> IC1S03 of A-K current down
--> IC1S03 Diode current down --> IC1S03 C-E current down --> IC1S03 C-E voltage up --> IC1SS2 F/B voltage
up --> Out Duty up --> Transformer 1st current up --> Transformer 1st power up --> Vout up --> Maintain Vout
5.8V
3) If load of 5.8 V terminal decreases(or AC input voltage rises) and Vout rises above 5.8V, then :
Reverse sequence of the above description --> Duty down --> Vout down --> Maintain 5.8V (i.e., the feedback
to maintains 5.8V).
ΠR1SS33, R1SS31 : Reduce 5.8V overshoot
´ R1SS32, C1SS27 : Prevent IC1S03 oscillation(for phase correction)
7-4
OCP
C
IC1S02
E
IC1S03
Trans D1SS13
C1SS35
R1SS31
A
K
K
2.5V
A
Fig. 7-8
L1SS05
C1SS16
R1SS33
C1SS27
R1SS32
R
2nd GND
5.8V
R1SS34
R1SS35