Samsung DVD-P360/CDM Service Manual page 82

13-1-2 Circuit description [FLY-Back PWM(Pulse Width Modulation)] Control
13-1-2 (a) AC Power Rectification/Smoothing Terminal
1) PDS01, PDS02, PDS03, PDS04 : Convert AC power to DC(Full wave rectification).
2) PER10 : Smooth the voltage converted to DC.
3) PCD01, PCD02, PBS01 : Noise removal at power input/output.
4) PVA1 : SMPS protection at power surge input.
13-1-2 (b) SNUBBER Circuit : PDS11, PCD12, PRS13, PCD11, PPS12
Vswitch
dt
0
13-1-2 (c) Driving circuit
When Vin supplied, driving current Ig occurs through the PIC1. By this I 1 (=Hfe x Ig) occurs throug the PIC1
and the Vb is inducted to base winding coil NB. By inducted Vb, Ib start flow and the V CC voltage of Pin 5
PWM IC is sustained stable. Ib is constant and I 1 increases in Proportion to time. After constant time passed Ib
become to shortage and PIC1 is cut OFF (S/W OFF).
Samsung Electronics
Inverted power
by leakage
inductance
Toff
Fig. 13-7
1) Prevent residual high voltage at the terminals of
switch during switch off/Suppress noise.
High inverted power occurs at switch (Pin 5 PWM
IC) off, because of the 1st winding of transformer :
(V=-L1 xdi/dt. L1 : Leakage Induction)
A very high residual voltage exist on both terminals
of PIC1 4, 5~8pin because dt is a very short.
2) SNUBBER circuit protects Pin 5 PWM IC
from damage through leakage voltage suppression
by RC, (Charges the leakage voltage to PDS11,
t
PER10, PCD12 and discharges to PRS12 , PRS13).
Circuit Operating Descriptions
13-3