Service manual

Service Manual
6
Electronic Circuit Theory
2.1 Inverter PWM circuit
2.1.1) Inverter Control circuit :( fig.2)
C5
1500pF/50V X7R
3.3V Lightest
C27
1nF/50V
C22
1500pF/50V X7R
CCFL_ON/ OFF
C1
0.1/50V
Q2
RK7002
1
32
U1
INL836
8
7
6
2
3
1
54
ISEN
DIM
VDDA
RT
GNDA
SST_CMP
DRV1DRV2
OVP
R1
open
Q3
2N3904
E
B
C
R17
33R
C9
470uF/25V
C21
1500pF/50V X7R
C12
22nF/25V
C8
1nF/50V
ON/OFF5
R18
33R
C6
33nF/50V
+5V
Q1
RK7002
1
32
R5 10K
DIM5
Q4 AP9971GD
1 2 3 4
6 7 8 5
S1 G1 S2 G2
D2 D1 D1 D2
C23
2.2uF/16V
R22
47K
+12V
C2
0.1/50V
ZD7
open
2
3
1
Brightness
3.3V On
R4
113K
0V of lightest
C25
open
0V Off
+5V
R3 10K
R7
1M
Fig.2
DC_5V through C23 and C2 will provide power for U1 on the pin6.
EN-ON/OFF voltage signal coming from scalar which is on IF BD will enable U1 to work.
During start up, The voltage of SST_CMP is determined by Pin8(ISEN).When ON/OFF signal is off,
MOSFET Q1 will be closed, then upper resister R22 give high signal to Q2’ GATE pin, and make
IC’Pin1(SST_CMP) to GND, so IC will shut down. If giving a high signal to Q1, Q2 will be
closed .then Pin1 will be floating. Once the voltage at the ISEN pin reaches the lamp on threshold,
the IC switches from the striking mode to the normal operation mode and the PWM dimming
control is activated. At the same time, the voltage of Pin1 will change following the voltage of Pin 8.
R5 is limited current resister and C6 accomplishes the soft start function.
DIM-ADJ duty cycle signal through R3 and C5 is on Pin 7(DIM), which will adjust IC’ output
duty cycle, then changing the brightness of Panel
The striking and operating frequency is determined by the external resistor (R4) connected to Pin
2. The striking frequency is 1.3 times of normal frequency.
DRV1 and DRV2 of U1 are used to drive Q4. DRV1 and DRV2 are controlled by build-in PWM
IC. DRV1 is reverse with DRV2.Q4 is built in 2 N-chanel MOSFET. DRV1 and DRV2’PWM signal