Samsung dvd-711, Service Manual

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Circuit Descriptions
Samsung Electronics 5-9
1) F/B terminal of PICF1 determines output duty cycle.
2) C-E(Collector-Emitter) of PICS1 and F/B potential of PICF1 are same.
◆
Operation descriptions
1) Internal OP-Amp ‘+’ base potential of PICS2 is 2.5V and external “-” input potential is connected with PRS33
and PRS34 to maintain Vout of 5.8V. (Vout = ((PRS38 x PRS34) / PRS34) x 2.5V)
2) If load of 5.8 V terminal increases(or AC input voltage decreases) and Vout decreases below 5.8V, then :
PICS2 “P” potential down below 2.5V --> PICS2 A-K of base current down --> PICS2 of A-K current down -->
PICS1 Diode current down --> PICS1 C-E current down --> PICS1 C-E voltage up --> PICF1 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).
ΠPRD31, PRD32 : Reduce 5.8V overshoot
´ PRS32, PCS32 : Prevent PICS2 oscillation(for phase correction)
5-2-2 (d) Feedback Control Circuit
PICF1
OCP
DRAIN
F/B
PICS1
C
E
1st GND
A
K
PICS2
A
2.5V
K
P
PRD31
PRS32
PCS32
2nd GND
PRS33
PRS34
PRD32
PES37
5.8V
PLS31
PDS33
PES33
Trans
GND
$
! @
#
%
VCC
Fig. 5-18