Dell ST2010 Service Manual page 9

Service Manual
power MOSFETs to regulate the CCFL current.
2.1.2 Output Circuit and Protection Circuit operations:(fig.3)
+13V
C25
+
680u/25V
The transformer (T1) secondary winding leakage inductance and output
capacitance(C31) forms a lower pass filter,which converts the square-wave driving
signal into a sinusoidal output voltage signal for CCFL.
The over-voltage protection feature is implemented by using an extermal
capacitor devider(C20/C21) to sense the output voltage.The divide-down voltage
signal is sent to the IC Pin11(VSEN) ,thus regulating the output voltage.
If a CCFL is removed, fails or damaged during normal operation, CCFL current
is no longer sensed and the voltage on ISEN pin drops. Once the voltage at the ISEN
pin is less than the lamp" on" threshold, the shutdown timer is activated. The IC
maintains the output voltage for approximately 2-3seconds and once the timer expires,
the IC will shutdown. To restart the IC, either toggle the SST_CMP pin or recycle the
power on the VDDA pin.
2.2 Power PWM circuit operations
2.2.1) Block diagram:(fig.4)
EMI Filter Rectifier and
filter
T1
DRV1
1 8
3 7
4
DRV2
6
DIP EEL19 SPW-054
Fig.3
Isolation power
transformer
8
C20
C22 3pF/3KV
12pF/3KV
VS1
C21
3pF/3KV
VS2
VS1
1
PIN1
2
+5V
PIN2
3
PIN3
4
PIN4
5
PIN5
6
PIN6
7
PIN7
8
PIN8
9
PIN9
10
PIN10
11
PIN11
12
PIN12 +13V
13
PIN13
DRV1
14
PIN14
15
PIN15
CN5
Rectifier and filter
Rectifier and filter
1
OP
2
R20
133
1
ISEN
2
R21
133
DIM/ON/OFF
PID
OP
ISEN
VS2
DRV2
Inverter circuit
AUDIO