Hitachi DV-P303U, Service Manual

Page: 52 / 106

Circuit Descriptions
6-3
6-1-2 Circuit description (FLY-Back Control)
6-1-2 (a) AC Power Rectification/Smoothing Terminal
1) PDS01,PDS02,PDS03,PDS04 : Convert AC power to DC(Wave rectification).
2) PE3 : Smooth the voltage converted to DC.
3) PCR01, PCR02, PCD01, PCD02, PCD03, PLS01, PBS01 : Noise removal at power input/output.
4) PVA1 : SMPS protection at power surge input (PVA1 pattern open is to remove noise).
6-1-2 (b) SNUBBER Circuit : PER11, PDS11, PCR11, PCD12, PRS11, PRS12
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 PQR11 because dt is a very short.
2) SNUBBER circuit protects PIC1 from damage
through leakage voltage suppression by RC,
(Charges the leakage voltage to PER11, PDS11, PCR11,
PCD12, and discharges to PR15 and PR16).
6-1-2 (c) Driving circuit
When Vin supplied, driving current Ig occurs throuhg the PRR11. By this IC (=HfexIg) occurs throug the PQR11
and the Vb is inducted to base winding coil NB of PQR11. By inducted Vb, Ib start flow and the PQR11 is saturated
(S/W ON). Ib is constant and Ic increases in propotion to time. After constant time passed Ib become to shotage
and PQR11 is cut OFF (S/W OFF).
Fig. 6-8 Driving Circuit