Service manual

Circuit Descriptions

6-4 Samsung Electronics

1) F/B terminal of PIC1 determines output duty cycle.

2) C-E(Collector-Emitter) of PIC2 and F/B potential of PIC1 are same.

3 Operation descriptions

1) Internal OP-Amp Ô+Õ base potential of PIC3 is 2.5V and external Ò-Ó input potential is connected with PR38 and

PR39 to maintain Vout of 5.8V. (Vout = ((PR36 x PR39) / PR39) x 2.5V)

2) If load of 5.8 V terminal increases(or AC input voltage decreases) and Vout decreases below 5.8V, then :

PIC3 ÔPÕ potential down below 2.5V --> PIC3 A-K of base current down --> PIC3 of A-K current down -->

PIC2 Diode current down --> PIC2 C-E current down --> PIC2 C-E voltage up --> PIC1 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).

Œ PR35, PR36 : Reduce 5.8V overshoot

´ PR37, PC44 : Prevent PIC3 oscillation(for phase correction)

ˇ PC09 : Adjust feedback response rate

6-1-2 (d) Feedback Control Circuit

PIC1

STR-G6153T

OCP

DRAIN

F/B

PC09

PIC2

1st GND

PIC3

2.5V

PR36

PR37

PC44

2nd GND

PR38

PR39

PR35

PC34

5.8V

PL34

PD33

PE33

Trans

GND

! @

VCC

Fig. 6-8