Switching Regulator Circuit; Rectifying And Smoothing Circuit; Auxiliary Power Supply Circuit - NEC MultiSync FP1370 Service Manual

8. SWITCHING REGULATOR CIRCUIT

8-1. Rectifying and Smoothing Circuit

AC input is rectified by D601. Then, it is smoothed by C610 and C609.
The resulting DC voltage is supplied to the converter circuit.
AC
AC

8-2. Auxiliary Power Supply Circuit

The auxiliary power supply circuit need to activate IC621. When the power switch is turn on, the current
flows into the capacitor C623 through R634, R635 and D602. Oscillation starts when the voltage of IC621
pin 9 reaches 8V by this action.
After the start of oscillation, the fly-back voltage of the auxiliary winding of T601 is rectified and smoothed
by D625,D623 and C623.
The resulting DC voltage is supplied to IC621 pin 9.
AC
D601
(Fig. 8-1) Rectifying and Smoothing Circuit
SW601
IC621
9
VIN
GND
2
C623
R625
(Fig.8-2) Auxiliary Power Supply Circuit
D601
C610
C609
+
+
- -
D602
Q623
R634
R635
+
ZD622
-
8-42
CONVERTER
CIRCUIT
D624
R636
+
R638
C624
-
D623 D625
L621 T601