Dell E2209Wf, Service Manual

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Service Manual
8
Over Voltage Protection and over-current protection are monitored by the voltage on VSEN(Pin
1) During normal operation , if a CCFL is damaged or removed ,the voltage at VSEN (Pin1)
increases .Once the voltage at VSEN exceeds 3.0V (OVPT Setting) the driver output duty cycle is
regulated and the shutdown delay timer is activated. OVPT set the overall protection threshold voltage
that is lower than 3V (VSEN threshold). Once the voltage at TIMER pin reached about 3v ,the IC will
shut down and latch . R3, R4,R14,R15,C1,C15,C16,C17 are connected in high voltage output
connector, the divided AC voltage is inverted DC voltage through D2, D3, R9 and C11 are used to
rectify wave & dump noise. Then the voltage signal reaches Pin1 VSEN of U1, when the voltage
changes, build-in PWM of U1 will adjust output voltage.
Open Lamp Protection: In normal operation, R10,R11 are sensed a high level DC voltage,If a
CCFL is removed or damaged during normal ,the voltage at SSTCMP(Pin2) rises rapidly .when the
voltage at SSTCMP reaches a threshold of approximately 2.0V,a current source charges the
capacitor(C3 and C18)connected to TIMER(Pin12).Once the voltage level at the TIMER pin reaches a
threshold of approximately 3.3v,The drive outputs shut down and latch .
2.2 Power PWM circuit
2.2.1) Block diagram:(fig.4)
2.2.2) AC Input and EMI Filter:(fig.5)
fig.5
CN850 is a connector for connecting AC Power. F850 is a fuse to protect all the circuit AC. Input
EMI Filter Rectifier and
filter Isolation power
transformer Rectifier and filter Inverter circuit
PWM controller
Switching element
Feedback Isolation
Rectifier and filter
Interface
circuit