Samsung DVD-P355B/XEH Circuit description FLY-Back PWMPulse Width Modulation Control

Circuit Operating Descriptions

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

Inverted power by leakage inductance

t

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 (PQR11) 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 PQR11 from damage through leakage voltage suppression by RC, (Charges the leakage voltage to PDS11, PER13, PCD12 and discharges to PRS11, PRS12).

13-1-2 (c) Driving circuit

When Vin supplied, driving current Ig occurs throuhg the PICF1. By this I1 (=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 VCC voltage of PQR11 is sustained stable. Ib is constant and I1 increases in Proportion to time. After constant time passed Ib become to shortage and PIC1 is cut OFF (S/W OFF).

Samsung Electronics 13-3