Samsung DVD-905, Service Manual

Page: 28 / 136

Reference Information
Samsung Electronics 2-9
7. Shut Off mode prevention circuit at instant load increase : PC15, PZD13
- During a sudden load increase;
By means of current concentration on specific output terminal, 5.8V voltage down
-->
F/B potential up
-->
Maintain Shut Off mode.
Stablize F/B potential (Loading completion) below 7V by lengthening CS potential rise time to 7V
(in order to prevent Shut Off mode).
- Normal operation : CS potential is 3.6V and PZD13(4.7V ZENER) is open.
- OD potential above 4.7V at instant load increase
-->
PZD13, PC15 work
-->
OS terminal condenser capacity
increases in parallel with PC14 and PC15
-->
CS potential rising rate down
-->
Instant operation completed
-->
F/B potential stable
-->
Normal operation
8. Maximum power limiting circuit addition : PZD11, PR19
- SMPS efficiency : Below 25W : High efficiency at AC110V input
Above 25W : High efficiency at AC230V input
- The peak value of current on switch at overload is lower than that at 110V input because SMPS is highly
efficient above 25W at 230V input. Therefore, maximum power increases at 230V as compared to
110V at overload. Add PZD11, PR19 and set to the same level as 110V.
- Higher at 230V input than at PZD11 input, limit maximum power because IS terminal potential goes up.
9. PQ1(F,E,T) Gate Drive Circuit : PR15, PR16, PD11
- PIC1 OUT is square wave but charging and discharing by PR15, PR16 occurs due to internal condenser
between gate-sources of PQ1.
- PR15, PR16 : Switch ON Time setting - PD11 is reverse : PIC1 OUT
-->
PR15
-->
PR16
-->
Charge to gate
- PR16, PD11 : Switch OFF Time setting - PD11 is proper : GATE - PR16
-->
PD11
-->
Discharge to PIC1
OUT(GND)
- Switch ON/OFF time : Releated to switch loss and noise
10. PIC1 overcurrent protection : PZD12
- Operate PZD12 and protect PIC1 from damage from residual overcurrent (PIC1 Vcc, due to external surge
inflow and feedback line open).