Samsung 2220WM - SyncMaster - 22" LCD Monitor Manual de servicio - Página 44
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Pin R of IC803 is supplied 2.5-v stable voltage. It connects to 5V and 14V output through R822,
R823 and R824. R822, R823 and R824 are output sampling resistor. When the sampling voltage more
than 2.5V or less than 2.5V, current of FB IC802 will change, this can change the voltage from T801.
12-3 IP Board Part(Inverter Part)
Inverter Circuit
1. R503, ZD501, R502, Q501 components convert +14V voltage into +5.0V voltage, and the voltage supply to
IC501. The extra PWM pulse signal (BRIGHTNESS signal) input to control IC through R512, R514, C510, The
LCT pin is set to a DC voltage of 0.7V by using a resistor divider(R507, R516), change the duty of PWM pulse,
will regulate the lamp current. The ON/OFF voltage connect to pin10 of IC501 through D501, R501, A voltage
of 2V to pin10 of IC501 enables the IC and activates the striking timer. The SSTCMP pin of IC501 performs the
soft function, the C511 set the time of SST. The operation frequency determined by external capacitor C512,
C521 and resistor R508 connected at CT pin of IC501. C515 connect the TIMER pin of IC501, the capacitor to
set striking time and shunt down delay time. DRV!, DRV2 output 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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