Service Manual
7
2.Electronic Circuit Theory
2.1 Inverter PWM circuit
2.1.1 Inverter Control circuit operations:(fig.2)
GND
DRV2
R11
100K
D1
BAV70
R8
33K
ISEN
PWM
+5V
CN5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PIN1
PIN2
PIN3
PIN4
PIN5
PIN6
PIN7
PIN8
PIN9
PIN10
PIN11
PIN12
PIN13
PIN14
PIN15
C7
2.7n
U1
INL816
1
2
3
4
5
6
12
13
14
15
16
7
8
9
10
11
DRV1
VDDA
SEL
RT1
RT
PWM
OLP1
OLP2
SSTCMP
GND
DRV2
PID
TIMER
ISEN1
ISEN2
VSEN
C2
10n
R10
20R
DRV1
+13V
R12
100K
DRV1
R3
10K
R7
33K
C3
2.2u
VS1
C6
OPEN
C8
2.7n
R6
NC
R1 10R
R13
10K
R9
20R
Q1
AP9971
1
2
3
4
5
6
7
8
.
.
.
.
.
.
.
.
DIM/ON/OFF
C9
3.3n
VS1
R4 560K
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PID
C5
47n
C10
3.3n
R5
191K
+5V
OP
+13V
R2 10K
C1
1u
VS2
Fig.2
DC_5V through R1 and C1 will provide power for U1 on the
pin2.PWM-ON/OFFandDIM voltage signal coming from scalar which is on IF BD
will PWM U1 to work. During start up, ISEN (pin9and pin10) senses the voltage on
the transformer secondary. If no current is sensed approximately 2 seconds, U1 shuts
off. R3 is used to limit current. C3 is used to dump noise, C5 is used to soft start, and
then the voltage on pin 14 will enable U1.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.
The striking and operating frequency is determined by the external resistor
(R4andR5) and connected to Pin 4and Pin5.
DRV1 and DRV2 of U1 are used to drive U2 . DRV1 and DRV2 are controlled
by build-in PWM IC. Q1 is switched which has two build-in IGBTs. The working
principle of circuit of T1, the same to circuit of Power.
The voltage signal on
negative
pole of D1 sensed through R7/R8 comes to
Pin11 of U1 VSEN (Lamp Current Detection & Control). The CCFL current is
detected through R12/R21 and reaches a regulated value. The CCFL current detected
at resistor R12/R21 is converted to a voltage level and input to the ISEN. Once the
CCFLs are ignited and current is sensed through resistor R12/R21, performs the loop
compensation function. The voltage at IC pin12 controls the drive duty cycle of the
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Страница 72: ...Service Manual 71 Attachment 3 PCB Layout Power inverter board Top Layer ...
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