Dell E1709W - Output Circuit and Protection Circuit

Service Manual
7
a DC voltage to PID (pin5).
The striking frequency is determined by R12 and C9 connected to Pin 13(CT) and R6
connected to RSTR (Pin6).The operating frequency is determined by R12 and C9 connected to Pin
13(CT) and R7 connected to RT (pin7).
DRV1 and DRV2 of U1 are used to drive U2. DRV1 and DRV2 are controlled by build-in PWM
IC. U2 is switch which has two build-in IGBTs.
2.1.2) Output Circuit and Protection Circuit :( fig.3)
OLP1
C19
3pF/3KV
R31
470R 1%
C35A
+12V
C33A
C21
470uF/25V
4100-D02 NC
CN2
1
2
WH-01
CN3
1
2
R32
470R 1%
C17
3pF/3KV
T1A
R19
610R
C15
ty pe 15pF/3KV NP0
C20
100pF/50V OPEN
D1 1N4148
ISEN1
C30
100pF/50V OPEN
T1B
4100-D02 NC
CN1
1
2
WH-02
CN4
1
2
D2 1N4148
T1
DIP EEL19 SPW-054
1
6
4
3
10
7
fig.3
The transformer (T1) secondary winding leakage inductance and output capacitance (C15)
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 external capacitor divider
(C17/C19) to sense the output voltage. The divide-down voltage signal is sent to the IC Pin9
(VSEN), thus regulating the output voltage.
The voltage signal on negative pole of D2 sensed through R19 comes to Pin4 of U1 (ISEN).
The CCFL current detected at resistor R19 is converted to a voltage level and input to the ISEN
pin.C6 is used to dump noise. Once the CCFLs are ignited and current is sensed through resistor
R19, capacitor C6 performs the loop compensation function. The voltage at IC pin12 (SSTCMP)
controls the drive duty cycle of the power MOSFETs to regulate the CCFL current.
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.