Detailed Description Of Each Circuit; Power Input Section; Lamp Drive Circuit Section - NEC LCD1550X Service Manual

1.8.4. Detailed description of each circuit

1.8.4.1

Power input section

J703
12V 1
R702
12V 2
1/16W 4.7K-J
R701
1/16W 4.7K-J
P_INV 5
R718
1/16W 220-J
The 12VDC output from the power board (PWB-POWER) is turned ON and OFF with the FET
switch (IC703), and is supplied to each oscillation circuit.
The IC703 (FET switch) is turned ON and OFF by turning Q705 (digital transformer) ON/OFF
with the signal (P_INVT) from the microcomputer.

1.8.4.2 Lamp drive circuit section

The lamp is driven with the self-exciting resonance circuit (royer circuit). For dimming, the
PWM (Pulse Width Modulation) method that changes the duty ratio by turning the switching
transistor base current ON and OFF is used.
Thus, the brightness can be changed with the Duty (PWM method) of PWM pulse signal (J703
pin 7: DUTYCINV) from ASIC.
12V
C707
R708
C710
C711
B50V
102-K
DUTYCINV
Iin
Source
1 8
2 7
3 6
4 5
Gate
IC703
HAT1021R
Q705
DTC143EKA-T
L701
R704
R703
R705
R709
Q706
R714
Q708
F701
Drain
F702
Q701
C701
Q702
1 - 44
Oscillation circuit 1
Oscillation circuit 2
T701
C703
SL6.3kV
15pF-J
C704
SL6.3kV
15pF-J