Samsung DVD-P191 Service Manual page 54

Schematic Diagrams
(d) Feedback Control Circuit
7-4
Fig. 7-3 Driving Circuit
Fig. 7-4
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u 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).
7-2-3 Internal Block Diagram
u Internal Block Diagram
Fig. 7-5
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