Samsung DVD-812 Service Manual page 47

Circuit Descriptions
◆ Advantages and disadvantages of linear power supply
1) Advantages : Little noise because the output waveform
of transformer is sine wave.
2) Disadvantages :
ΠAdditional margin is required because Vs is chan-
ged (depending on power source). (The regulator
loss is caused by margin design).
´ Greater core size and condensor capacity are ne-
eded, because the transformer works on a single
power frequency.
5-1-1 (b) S.M.P.S. (Pulse width modulation method)
Vin
◆ Terms
1) 1st : Common power input to 1st winding.
2) 2nd : Circuit followings output winding of transformer.
3) f (Frequency) : Switching frequency (T : Switching cycle)
4) Duty : (Ton/T) x 100
5-2
+
Switch
+
Vs switch
–
ON/OFF Control
I switch
v
Vreg
0
Transformer
(Np) (Ns)
+ +
(Vp) (Vs)
– –
Fig. 5-6
Change by common power
Vout
Regulator loss
Fig. 5-5
Vout
REGULATOR
+
Samsung Electronics
t