Circuit Description Of Power Supply Pwb - Sharp FO 4400 - B/W Laser - All-in-One Service Manual

[6] Circuit description of power supply PWB

This unit supply input AC 120 V/60 Hz, +24 V, +5 V as block diagram
shows. (See Fig. 11)
F702
4A/125V
AC-L
AC-N
F701
FG
8A/125V
HEATER
HEATER
ON/OFF
CIRCUIT
1. Noise/Rectification and smoothing circuit
Filter part reduces the outgoing noise that generated in the Power Sup-
ply unit, and prevents the invasion of the noise from outside. The exces-
sive surge such as the thunder is prevented by Varistor X701.
Rectification and Smoothing circuit is supply DC voltage to switching
part by AC input rectify by Diode D701, D702, D703, D704 and smooth-
ing Capacitor C706.
2. Switching circuit
This circuit is adopt Ringing Choke Converter system that self-excited.
This system supplies power as follows;
AC voltage that supplied by Rectifying and smoothing part is change
high-frequency pulse by NO/OFF repeat of MOS FET Q701. And while
Q701 ON, accumulate energy in primary winding of transformer T701.
And while OFF, eject energy to secondary winding.
Control of constant voltage is carry out by as follows;
Feedback put on control circuit through photo coupler from +24 V Out-
put. Over Current Protection Circuit detect spread of ON period by Out-
put Load is heavy, and extend OFF period by control circuit. And turn
down energy that accumulating in primary winding.
Over Current Protection is make secondary side of output voltage
+24 V's rising over voltage condition by conducting Zener Diode D711
that between +24 V output and GND. Then protection is carrying out by
Over Current Protection Circuit of Control Circuit working.
NOISE CIRCUIT/
RECTIFICATION AND
SMOOTHING CIRCUIT
T701
SWITCHING
CIRCUIT
CONTROL
CIRCUIT
PC701
PC702
RL701
Fig. 11
3. +24 V circuit
+24 V Circuit is supplied by Transformer T701 Output Rectification and
Smoothing by Diode D710, Capacitor C715.
4. +5 V circuit
+5 V Output is carry out stabilization by step-down Chopper Circuit that
inputted above +24 V. When MOS FET Q705 ON, this system supply
load energy through L705, and when OFF, accumulated energy in L705
Rectification to load by D715. Control of constant voltage is carry out by
detect +5 V output by Shunt Regulator and put on Feedback.
5. HEATER ON signal
HEATER ON/OFF is carry out by send a signal through Trigger TR701
of Photo Triac Coupler PC702 by (High/Low).
6. HEATER-RELAY OFF signal
ON/OFF of Relay RL701 is carry out by (High/Low). But when HEATER-
RELAY OFF Signal change High to Low, Thyristor SR701 keep ON con-
dition. So RL701 keep OFF condition till Power Supply re-inter.
5 – 19
F703
4A/125V
+24 V CIRCUIT
SWITCHING +5 V
CIRCUIT CIRCUIT
CONTROL
CIRCUIT
FO-4400U
FO-CS1
+24 V
F704
4A/125V
+5 V
GND