Electronic Circuit Theory - Dell 2209WA Service Manual

Service Manual

Electronic Circuit Theory

2.1 Inverter PWM circuit
2.1.1)Inverter Control circuit:(fig.2)
4.1
ON/OFF voltage signal coming from IF BD will enable U1 to work.C2 is
used to dump noise.
During the striking period, if the voltage at VSEN_POL(pin12) reaches a
threshold of approximately 2.85V, the transformer output voltage will be
regulated until the striking timer expires.
During normal operation, if the voltage at VSEN_POL(pin12) reaches the
present voltage at OVPT(pin16), the sink and source current of
SSTCMP(pin14) will stop and the TIMER(pin15) will be charged. Once
TIMER(pin15) expires and the abnormal condition still exists, U1 will
shutdown and latch.
Once the IC is enabled, when the voltage at VREF(pin21) rises to
approximately 4.0V, before the transformer output is present, and voltage at
Fig.2
8