ViewSonic VG720 - 17" LCD Monitor Service Manual page 17

4.3 PWPC BOARD BLOCK FUNCTION DESCRIPTION
PWPC board combines to adapter and inverter, Adapter which commonly consists
of bridge rectifier and filter, start circuit, PWM control circuit, protection circuits and
convert to 12V, 5V DC voltage by input 90V-240V AC voltage that provide power supply
for each chips in the main board and inverter. Inverter is DC TO AC circuit. It changes
the 12v DC of power supply to about 600-800v AC that drives the backlight. It mostly
consists of starting circuit, PWM controller, DC changing circuit, LC surging circuit,
output circuit and protection circuit etc.
AC input
EMI filter
Lamp
Feedback
Circuit
ViewSonic Corporation
Bridge
Rectifier
and Filter
Start Circuit
R903, R904,R905
PWM
Control IC
OSC and
DC Convert
Output
Circuit
Circuit
Over
Voltage
Rectifier
Transformer
CMOS
MOSFET
Q203
PWM
Control IC
- 17 –
Confidential - Do Not Copy
Over
12V
Voltage
Protect
ON/OF
ON/OFF
Control
DIM
CN902
5V
VG720