Canon LBP-1120 Service Manual page 31

CHAPTER 2
D. Low-Voltage Power Supply Circuit
1. Outline
The AC voltage input from the inlet is converted into the DC voltage in the rectification circuit, transformer, and power
supply circuits. Then, the DC voltage is supplied to the printer as +24VDC, +5VDC, and +3.3VDC.
When the cartridge door is opened, the door switch (SW301) is turned OFF. This cut OFF the +24VU supplied to
the high-voltage circuit. At the same time, the DOSNS signal goes "L", causing the CPU to determine that the cartridge
door is opened and to stop the printer.
The AC voltage is supplied to the fixing heater through the fuse (FU101), noise filter, relay, and triac.
The +3.3VDC is supplied to the ICs on the engine controller PCB, BD PCB, and interface controller PCB.
The +5VDC is supplied to the ICs on the engine controller PCB, laser/scanner driver PCB, interface controller PCB,
and sensors.
The +24VDC is supplied to the high-voltage power supply circuit, main motor, scanner motor, and solenoids.
Inlet
Fuse
(FU101)
Noise
filter
Fuse
(FU102:100-127V only)
Noise
filter
Rectifi-
cation
circuit
Control IC
Transformer
(T501)
(IC501)
Overvoltage
detection
circuit
Overcurrent
detection
circuit
2 - 12
Engine Controller PCB
Relay
Triac
DOSNS
CPU
Door switch
(SW301)
+24V
power
supply
+24V
circuit
+24V
+24V
+24V
+24V
+5V
+5V
power
supply
circuit
+3.3V
power
supply
circuit
Figure 2-2-6
High-voltage
power supply
circuit
+24VU
Main
motor
drive
circuit
+5V Laser/scanner
+3.3V
+5V
+3.3V
+5V
+5V
Sensor
Fixing heater
Main motor
Solenoid
unit
Interface
controller
PCB
Sensors