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Acer
Service Manual
for power MOSFET U501, U502.
2. OZ9938 provides two drive signals for U501, U502, and they work in push pull topology driving, two
transformers are connected in parallel with each transformer driving two lamps in series. Turning each
N-Channel MOSFET "on/off" complementarily, produces an alternating current through the transformer
primary and secondary. The "on" duration of the switches determines the amount of energy delivered to the
CCFLs. R504, C504, R505, C505, R532, C529, R530, C522 are snubber networks, they suppress Voltage
transient spike in drain of power MOSFET.
3. R506, R510, C509, C513, C514, R525, R531, C528, C525, and C527 are connected between high voltage
output connector and ground, the divided AC voltage is inverted DC voltage through D502, D503, D508,
and D509. The sense voltage feed back to VSEN (pin 6 of IC501) for an over voltage/over current condition
during normal operation. R528, R533 are current sense resistor, current sense signal feed back to Isense (pin
5 of IC501) for lamp "ON" detection.
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