Samsung DVD-907, Service Manual

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Circuit Descriptions
Samsung Electronics 7-3
Circuit Descriptions
7-2 Samsung Electronics
3 Advantages and disadvantages of linear power supply
a. Advantages :
Little noise because the output waveform of transformer is
sine wave.
b. Disadvantages :
» Additional margin is required because Vs is changed
(depending on power source). (The regulator loss is
caused by margin design).
» Greater core size and condensor capacity are needed,
because the transformer works on a single power
frequency.
Fig. 7-5
7-1-1(B) SMPS(PULSE WIDTH MODULATION METHOD)
Fig. 7-6 SMPS
3 Terms
- 1st : Common power input to 1st winding.
- 2nd : Circuit followings output winding of transformer.
- f(Frequency) : Switching frequency(T : Switching cycle)
- Duty : (Ton/T) x 100
V
Vreg
Vout
0
t
Change by common power
Regulator loss
Transformer Vout
(Np)
(Vp)
Switch
Vs switch
I switch
Vin
ON/OFF Control
+
–
+
–
+
+
+
–
(Vs)
(Ns)
Regulator
7-1-2 Circuit description(FLY-BACK PWM(Pulse Width Modulation) control)
7-1-2(a) AC power rectification/smoothing terminal
- PD01,PD02,PD03,PD04 : Convert AC power to DC(Wave rectification)
- PO03 : Smooth the voltage converted to DC(Refer to VIN of Fig. 7-7)
- PC01, PC02, PC10, PC11, PC12, PC13, PL01, PL02, PL03 : Noise removal at power input/output
- PVA1 : SMPS protection at power surge input
(PVA1 pattern open is to remove noise)
- PR10 : Rush current limit resistance at the moment of power cord insertion.
» Rush current = (AC input voltage x 1.414 - Diode drop voltage) / Pattern resi PL02,01
resi PC10 resi PR10) (AC230V based : approx. 26A)
» Without PR10, the bridge diode might be damaged as the rush current increases.
7-1-2(b) SNUBBER circuit : PR15, PR16, PC04, PD05, PD11, PR17
- 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=L1xdi/dt. LI : Leakage Induction)
A very high residual voltage exists on both
terminals of PIC1 because dt is a very short.
- 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).
- PC05, PL17 : For noise removal
Fig. 7-7
7-1-2(c) PIC1 Vcc circuit
- PR11, PR12, PR13, PR14 : PIC1 driving resistance (PIC1 works through driving resistance at power cord in)
- PIC1 Vcc : PR18, PD12, PC06
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 PC06.
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.)
0
Vswitch
dt
Toff
t
Inverted power
by leakage
inductance