ViewSonic VG720 - 17" LCD Monitor Service Manual page 21

NCP1203D60R2G (IC901): PWM control, high-voltage startup current. The circuit unit
has functions such as over-current protection, over-voltage protection, output
short-circuit protection and etc. The function of each pin and the inside circuit diagram
are as follows:
Pin Pin
No. Name
Adjust the skipping
1 Adj
2 FB
3 CS Current sense input
4 GND
5 Drv
6 VCC
7 NC
Ensure a clean and
8 HV
ViewSonic Corporation
Function
peak current
Sets the peak
current setpoint
The IC ground
Driving pulses
Supplies the IC
−
lossless startup
sequence
This pin lets you adjust the level at which the cycle
skipping process takes place. Shorting this pin to ground,
permanently disables the skip cycle feature.
By connecting an optocoupler to this pin, the peak current
setpoint is adjusted accordingly to the output power
demand. Skip cycle occurs when FB falls below Vpin1.
This pin senses the primary current and routes it to the
internal comparator via an L.E.B.
−
The driver's output to an external MOSFET.
This pin is connected to an external bulk capacitor of
typically 22 F.
This unconnected pin ensures adequate creepage
distance.
Connected to the high−voltage rail, this pin injects a
constant current into the VCC capacitor during the startup
sequence.
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Pin Description
Confidential - Do Not Copy VG720