Sub Switching Regulator Circuit - NEC MultiSync LCD2080UX -BKA Service Manual

2.9.10 SUB Switching Regulator Circuit

After the AC power switch (SW901) is turned on, the charging current flows into the capacitor C905 through
terminal "C"(control) from "D"(drain) of IC9A1. MOS FET is built in by IC9A1.
Oscillation starts when the voltage of C9A4 reaches 5.9V by this charging operation.
After the start of oscillation, the voltage of secondary output is raised. At the same time, the fly-back voltage
of auxiliary winding of T9A1 is rectified and smoothed by D9A2 and C9A2.
The resulting DC voltage is supplied to PC9A1.
SUB switching regulator have the error detection amplifier circuit.
The output of the error detection amplifier circuit is feed back to IC9A1 terminal "C" via PC9A1 to control the
duty cycle of built-in switching devices. In result, the output voltage is kept constant.
Intermittent oscillates at a light load, and the oscillation period shortens.
The period which oscillates by the load heavy becomes long.
The drain current is regulated by peak current control.
The drain electric current is detected the "Vds" turn ON pulse by pulse.
It is detected by the resistance of "Ron" of MOS FET.
When a Vds exceeds regulation value, it stops until the next oscillation period.
C906+
D
IC9A1 C
S
C906-
C9A3 R9A2
D9A1
D9A2
PC9A1
C9A2
C9A4
(Fig.2.9.10) SUB Switching Regulator Circuit
T9A1
D9E1
1
6
C9E1
3 8
5
4
7-17
L9E1 5VA
R9E2
R9E1
R9E3
PC9A1
C9E2
IC9E1
R9E4
C9E3
GND