Samsung DVD-HD850/XAA, Service Manual, Page: 75 / 94

Circuit Operating Descriptions
Samsung Electronics 13-5
◆
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 4.4V.
2) If load of 4.4V terminal increase (or AC inout voltage decrease) and Vout decrease over 4.4V,
Then : PICS2 “R” potential decrease over 2.5V --> PICS2 A-K BASE Current decrease --> PICS2 A-K Current
decrease --> PICS1 DIODE Current decrease --> PICS1 C-E Current decrease --> PICS1 C-E Voltage increase -->
PICS1 F-B Voltage increase --> OUT DUTY increase TRANS Primary Cuttent Increase --> TRANS Primary
Power increase --> Vout increase --> Vout maintain 4.4V
- PRD31, PRD32 : Reduce 4.4V overshoot.
- PRS32, PCS32 : Prevent PICS2 oscillation (for phase correction).
13-1-2 (d) Feedback Control Circuit
GND
PICF1
Icease
R
C
R
FB
C
Softs
POWER-CTL
Mos-Fet
Drain VCC
Ib
R
D
C
Ig R
Vin
Snubber
NP
Ig
VB
VB
PTDI
Ns
Vs
I2
PDS34
PES34
+
Vout
GND
+
A
K
Fig.13-9