Samsung DVD-739, Service Manual

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Circuit Descriptions
Samsung Electronics 6-3
6-1-2 Circuit description (FLY-Back PWM (Plise Width Modulation) Control)
6-1-2 (a) AC Power Rectification/Smoothing Terminal
1) PD01,PD02,PD03,PD04 : Convert AC power to DC(Wave rectification)
2) PE3 : Smooth the voltage converted to DC(Refer to VIN of Fig. 6-7)
3) PC01, PC02, PC10, PC11, PC12, PC13, PL01, PL02, PL03 : Noise removal at power input/output
4) PVA1 : SMPS protection at power surge input (PVA1 pattern open is to remove noise)
5) PR10 : Rush current limit resistance at the moment of power cord insertion.
Œ
Rush current = (AC input voltage x 1.414 - Diode drop voltage) / Pattern resi PL02,01 resis-
tance + PC10 resi PR10) (AC230V based : approx. 26A)
´
Without PR10, the bridge diode might be damaged as the rush current increases.
6-1-2 (b) SNUBBER Circuit : PR15, PR16, PC04, PC05, PD11, PR17
0
Vswitch
dt
Toff
t
Inverted power
by leakage
inductance
Fig. 6-7
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 PIC1 because dt is a very short.
2) SNUBBER circuit protects PIC1 from damage
through leakage voltage suppression by RC,
(Charges the leakage voltage to PD11 and PC04, and
discharges to PR15 and PR16).
3) PC05, PR17 : For noise removal
6-1-2 (c) PIC1 Vcc circuit
1) PR11, PR12, PR13, PR14 : PIC1 driving resistance (PIC1 works through driving resistance at power cord in)
2) PIC1 Vcc : PR18, PD12, PE6
Œ
Use the output of transformer as Vcc, because the current starts to flow into transformer while PIC1 is active.
´
Rectify to PD12 and smooth to PE6.
ˇ
Use the output of transformer as PIC1 Vcc : The loads are different before and after PIC1 driving.
(Vcc of PIC1 decreases below OFF voltage, using only the resistance due to load increase after PIC1 driving.)