Electronic Circuit Theory - Dell ST2010 Service Manual

Service Manual

2.Electronic Circuit Theory

2.1 Inverter PWM circuit
2.1.1 Inverter Control circuit operations:(fig.2)
R1 10R
+5V
R13
10K
R2 10K
DIM/ON/OFF
R3
PID
10K
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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
+13V
U1
1
DRV1 DRV2
C1
1u 2
VDDA GND
3
SEL SSTCMP
R4 560K
4
RT1 OLP2
5
RT OLP1
R5 PWM 6
PWM VSEN
191K C2 7
PID ISEN2
10n
8
TIMER ISEN1
C3 INL816
2.2u
R6 C6
NC OPEN
Fig.2
7
R10
20R
Q1 C10
3.3n
3 5
. .
4 6
. .
1 7
. .
2 8
. .
AP9971
16
15
14
C5
13 47n
R11
OP
12 D1 BAV70
100K
11
VS1
10
R12
ISEN
9 R7 C7
100K 33K 2.7n
R9
20R
C9
3.3n
DRV2
DRV1
1
PIN1
2
PIN2
3
PIN3
4
PIN4
5
PIN5
6
PIN6
7
PIN7
8
PIN8
9
PIN9
10
PIN10
11
PIN11
12
VS2
PIN12
13
PIN13
14
PIN14
15
PIN15
R8 C8
33K 2.7n
CN5
GND
VS1
+5V
+13V
DRV1