NEC AccuSync LCD72VM User Manual page 121

Rectifier and filter circuit: The AC input is changed to a high DC voltage. The magnitude is a product of 1.414
to AC after it is converted by a bridge rectifier (BD901) and filtered by the capacitor (C905).
Start-up circuit: After being converted and filtered, the high DC voltage travels through R906, R907 as they
dissipate a portion of the voltage. Start-up begins when the lowered voltage is supplied at a current of 30uA to
IC901 (SG6841D). The output pulse makes the switch-power circuit work. The voltage produced at the two
terminals of T901 is sent to PIN 7 of IC901 after being commuted by D902 and filtered by C907. The start-up
process is ended.
SG6841: PWM. It requires low start-up current (30uA) and low working current (3mA). It contains functions
such as low-voltage protection, over-current protection, over-voltage protection, Temperature protection, etc. The
function of each pin and the inside circuit diagram are as follows:
Pin NAME
1 GND
2 FB
3 VIN
4 RI
FUNCTION
Ground
Feedback voltage input
Start-up current input
Reference setting
Pin NAME
5 RT Temperature protection
6 SENSE Current test pin
7 VDD Power supply
8 GATE PWM drive output
7-6
FUNCTION