Acer AL1717 Service Manual page 9

Acer
14VDC provides the power for IC501; the control signals Brightness and ON/OFF come from I/F
board. ON/OFF signal connect to pin8 of IC501 and makes IC501 enable. Brightness signal connect to
pin7 of IC501 and regulates the panel brightness, R526, D515, R529, C505 make up a network of
delaying time circuit and R523, R524 make up a divided voltage network, C504 is used to dump noise.
The operation frequency is determined by the external Resistor R522 and capacitor C529 connected to
pin5 of IC501. BURST MODE dimming pulse frequency and duty is regulated by I/F board. C503 is
used for soft start and compensation, C502, C528 are used for dump noise.
The output drives, include NDR4, NDRV2, PDRV3, PDRV1 (pins1, 3, 15, 16 respectively) output
square pulses to drive MOSFET U501, U502, and each of U501, U502 is consist of a N channel
MOSFET and a P channel MOSFET. U501 and U502 work as full-bridge topology, it is high efficient,
zero voltage switching.
During start up, VSEN (pin9) senses the voltage at the transformer secondary. When VSEN reaches
3.0V, the output voltage is regulated. If no current is sensed approximately 1.5 seconds IC501 shunt off.
The current flowing through CCFL is sensed and regulated through sense resistor R509, R511. The
feedback voltage through R506, R507, C508 connected to Pin11 (ISEN), then compared with a
reference voltage (1.5V) via a current amplifier, resulting in PWM drive outputs to full-bridge switches.
4.2 Protection circuit
Over Voltage Protection: R501and R502 are connected in high voltage output connector, the
divided AC voltage is inverted DC voltage through D508, R505 and C507are used to rectify wave &
dump noise. Then the voltage signal reaches Pin9 VSEN of IC501, when the voltage changes, build-in
PWM of IC501 will adjust output voltage.
Open Lamp Protection: In normal operation, the resistors R510, R511, R512, R509 are sensed a
high level AC voltage, the AC signal OP1 invert DC voltage through D509, R515, C533, and the high
level DC voltage reaches the gate pin of Q502, similarly, the gate pin of Q503, Q504, Q505 has high
level DC voltage. So the gate pin of Q501 has a low level voltage, and the IC501 is normal operation.
Once one of signal OP1, OP2, OP3, and OP4 is low, the voltages of Q501 gate pin is high level, and
make the voltage of ISEN low level, the IC501 will be shunt down.
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Service Manual