Acer P221W Service Manual page 9

Acer
4.1 Low voltage to high voltage circuit
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