ViewSonic VA1721WMB - Page 19

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ViewSonic Corporation
Confidential - Do Not Cop VA1721wmb
Circuit Diagram
LD7552BPS (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 Name Function
1 GND Ground
2 COMP
Voltage feedback pin (same as the COMP pin in UC384X), By
connecting a photo-coupler to close the control loop and achieve the
regulation
3 VCC Supply voltage pin
4 RT
This pin is to program the switching frequency. By connecting a resistor
to ground to set the switching frequency.
6 NC Unconnected pin
7 VCC Supply voltage pin
8 OUT Gate drive output to drive the external MOSFET