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65

This power supply board uses the switching regulator method.

The input current goes into the input rectifier circuit through the filter circuit. The filter circuit decreases the noise voltage and the
noise electric field strength.

The input current is rectified by D10~ D13 and charges C5 to make DC voltage. Then it supplies power to the converter circuit.

Bias is applied to the Q1 gate via this circuit when the AC power is turned on and Q1 begins operating.

Input
Circuit

AC
Input

F2

F1

Surge
absorber
circuit

G

+5V

+24V

Kick-on
Voltage
Circuit

E

F

PG

+4V

HTRCTL

Control
Circuit

R2

R3

Converter
Circuit

C

D

5V
Output
Circuit

24V
Output
Circuit

Rectifier
Circuit
D10-D13

A

B

C5

Error Detecting
Circuit

   O.C.L
   Over voltage

Q1

A-B Voltage Wave Form

C-D Voltage Wave Form

E-F

G-H Voltage Wave Form

0

0

0

CN1

CN2

T1

PC1

IC501

Triac
SCR1

Heat Lamp

Photo Triac
Caupler PC2

R4

R41

H

DG

4V
Output
Circuit

IC401

C401

C501

D401

D501

C101

D101

66

The following is an overview of how the power supply unit is controlled. 
The control method of this power supply unit is pulse width modulation.

When Q

1

 is ON, the energy is charged in the transfer primary coil according to E

1

. When Q

1

 is OFF, the energy is output from

the secondary transfer as follows.
    L 

→ D

1

 

→ Load → L

Then the power is supplied to the Load. When Q

1

 is ON, power is not output from the secondary side. The output voltage is fed

back in the control IC according to the error amp rectifier. Then depending on how T

ON

 is controlled, stabilization occurs. Also,

when the current load becomes too large, in order to decrease the voltage output, the increase in   is controlled and the output
voltage is stabilized.
Therefore, basically the timing: Ton/Toff of Q1 controls the output voltage.

67

This circuit is for absorbing surge voltage generated by the transformer.

The control circuit amplifies the output with increased voltage detected in the error detecting circuit. Then it drives the main tran-
sistor.
In this power supply, the duty ratio is defined by changing the ON period of the main transistor.
This is shown as follows.
When the output voltage of the 24V circuit increases, the current of the photo coupler PC1 increases, the pulse width of the out-
put control IC becomes narrower and the ON period of Q1 becomes shorter.

The highest drain current (Q1) is limited by a limiter circuit of 24V. The 24V output is limited by this circuit.

If the 24V output increases because the error detecting circuit or control circuit is broken, Control Circuit will recognize this sig-
nal and output becomes 0V. D104 and D504 also prevent over voltage.

Refer to Power Supply Board Section (P.65).

68

*1 The paper stacker and document stacker may not be
shown in all illustrations.