Samsung DVD-905, Service Manual

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Reference Information
Samsung Electronics 2-5
2-1-2 SMPS circuit description
2-1-2(a) CIRCUIT METHOD
FLY-BACK PWM(Pulse width modulation) control
2-1-2(b) CIRCUIT DESCRIPTIONS
1. AC power rectification/smoothing terminal
- PD01 : Convert AC power to DC(Wave rectification)
- PO10 : Smooth the voltage converted to DC(Refer to Vin of Fig. 2-7)
- PC01, PC02, PC03, PC04, PC05, PC06, PL01, PL02, PL03 : Noise removal at power input/output
- PVA1 : SMPS protection at power surge input
- PVA2 : SMPS protection at 2st ground surge input(PVA1 pattern open : to remove noise)
- PR10 : Rush current limit resistance during power cord insertion.
È Rush current = (AC input voltage x 1.414 - Diode drop voltage) / Pattern resi PL02.01
resi PC10 resi PR10) (AC230V based : approx. 26A)
È Without PR10, the bridge diode might be damaged as the rush current increases.
2. SNUBBER circuit : PR17, PR18, PC11, PD10
- Prevent residual high voltage at the terminals of
switch during switch off/Suppress noise.
High inverted power occurs at switch off,
because of the 1st winding of transformer:
(V=L1xdi/dt. LI : Leakage Induction)
A very high residual voltage exists on both
terminals of PQ1 because dt is a very short.
- SNUBBER circuit protects PQ1 from damage
through leakage voltage suppression by RC,
(Charges the leakage voltage to PD10 and PC11,
and discharges to PR17 and PR18).
- PC12, PL11 : For noise removal
Fig. 2-16
3. PIC1 Vcc circuit
- PR11, PR12, PR13, PR14 : PIC1 driving resistance (PIC1 works through driving resistance at power cord in)
- PIC1 Vcc : PR20, PD12, PC17
1) Use the output of transformer as Vcc, because the current starts to flow into transformer while PIC1 is active.
2) Rectify to PD12 and smooth to PC17.
3) 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.)
- PR20 : For noise removal
0
Vin–Vp
Vswitch
dt
Toff
t
Inverted power
by leakage
inductance