Second Auxiliary Power Supply Circuit; Second Converter Circuit - NEC MultiSync FP1370 Service Manual

8-12. Second Auxiliary Power Supply Circuit

The second auxiliary power supply circuit need to activate IC651. When the power switch is turn on, the
current flows into IC651 pin3.
And the current which flowed out from IC651 pin1 charges C653.
Oscillation starts when the voltage of IC651 pin 1 reaches about 6V by this action.
After start of oscillation, the fly-back voltage of the auxiliary winding of T651 is rectified and smoothed by
D651,R651 and C651.
The resulting DC voltage is supplied to IC651 pin 1.(Then current frows in into IC651 pin 1.)
D601(+)
C610

8-13. Second Converter Circuit

The second converter circuit consists of the primary winding of T651,
a switching device MOSFET(internal IC651) and surge absorbers (C656,C660,R659,R660 and D653)
which are connected to the primary winding of T651.The feedback current to control "ON Duty" flows in
into IC651 pin 1. so that the collector-emitter is turned ON and OFF.
IC651 pin 1 is also used as the connection to provide internal bias current.
D601(+)
C610
Feedback Current
+ +
- -
C609
3
DRAIN
CONTROL
IC651
SOURCE
2
C654
(Fig.8-13) Second Auxiliary Power Supply Circuit
+ +
- -
C609
C
1
R657
+
C653
-
(Fig.8-14) Second Conveter Circuit
PC651
1
R658
R657
+
C653
-
C660
D
IC651
3
PWM
Control
Circuit
2
S
8-51
R651
D651
C651
+
-
R660
T651
D653
R659
C656
T651