Samsung DVD-812 Service Manual page 48

5-1-2 Circuit description (FLY-Back Control)
5-1-2 (a) AC Power Rectification/Smoothing Terminal
1) PDS01, PDS02, PDS03, PDS04 : Convert AC power to DC(Wave rectification).
2) PE3 : Smooth the voltage converted to DC.
3) PCR01, PCR02, PCD01, PCD02, PCD03, PLS01, PBS01 : Noise removal at power input/output.
4) PVA1 : SMPS protection at power surge input (PVA1 pattern open is to remove noise).
5-1-2 (b) SNUBBER Circuit : PER11, PDS11, PCR11, PCD12, PRS11, PRS12
Vswitch
dt
0
Toff
5-1-2 (c) Driving circuit
When Vin supplied, driving current Ig occurs throuhg the PRR11. By this IC (=HfexIg) occurs throug the PQR11
and the Vb is inducted to base winding coil NB of PQR11. By inducted Vb, Ib start flow and the PQR11 is saturat-
ed (S/W ON). Ib is constant and Ic increases in propotion to time. After constant time passed Ib become to
shotage and PQR11 is cut OFF (S/W OFF).
Samsung Electronics
Inverted power
by leakage
inductance
Fig. 5-7
1) Prevent residual high voltage at the terminals of
switch during switch off/Suppress noise.
High inverted power occurs at switch (PIC1) off,
because of the 1st winding of transformer :
(V= LI xdi/dt. LI : Leakage Induction)
A very high residual voltage exists on both terminals
of PQR11 because dt is a very short.
2) SNUBBER circuit protects PIC1 from damage
through leakage voltage suppression by RC,
(Charges the leakage voltage to PER11, PDS11, PCR11,
PCD12, and discharges to PR15 and PR16).
t
Fig. 5-8 Driving Circuit
Circuit Descriptions
5-3