ViewSonic VG920-1 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
Sets the peak
2 FB
current setpoint
3 CS Current sense input
4 GND The IC ground
5 Drv Driving pulses
6 VCC Supplies the IC
7 NC
Ensure a clean and
8 HV lossless startup
ViewSonic Corporation
Function
This pin lets you adjust the level at which the cycle
skipping process takes place. Shorting this pin to ground,
peak current
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
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 sequence.
Pin Description
F.
Confidential - Do Not Copy
18
VG920-1