Acer Service Manual
3.2 Protection circuit
Over Voltage Protection: C503, C505and C506 are connected in high voltage output connector,
the divided AC voltage is inverted DC voltage through D503, R523and C533 are 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 test points of OP1, OP2, OP3, OP4, OP5, OP6
are sensed a high level AC voltage, the AC signal, for example OP1 invert DC voltage through R531,
C540, so the high level DC voltage reaches the gate pin of Q502, So the gate pin of Q501 has a low
level voltage, and the IC501 is normal operation. Once one of signal OP1, OP2, OP3, OP4, OP5 and
OP6 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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