Dell 2209WA Service Manual page 11

Service Manual
The transformer (T1 to T12) secondary winding leakage inductance and
output capacitances that are in the inverter PCB board, forms a lower pass
filter, which converts the square-wave driving signal into a sinusoidal output
voltage signal for CCFL.
The voltage signal sensed through R14 comes to Pin13 of U1-ISEN (Lamp
Current Detection & Control). The CCFL current is detected through R14 and
reaches a regulated value. The CCFL current detected at resistor R13 and
R14 is converted to a voltage level and input to the ISEN pin. 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.
C21 is used to dump noise. Once the CCFLs are ignited and current is
sensed through resistor R14 ,capacitor C15 performs the loop compensation
function. The voltage at pin1, pin2, pin23 and pin24 controls the drive duty
cycle of the power MOSFETs to regulate the CCFL current.
Q5 off and Q6 on during normal operation. Once any one of ISs falls down,
gate of Q6 lost voltage, Q6 turns off and Q5 turns on, ISEN would be pulled
Fig.3
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