Low-Voltage Power Supply; Circuit - Canon LBP-1000 Service Manual

CHAPTER 2
D. Low-voltage Power Supply Circuit
1. Outline
AC power is supplied to the low-voltage power supply circuit in the engine controller when the
power switch (SW201) is turned ON.
The low-voltage power supply circuit supplies +24VDC and +3.3VDC required for the printer.
+24VDC is supplied to the high-voltage power supply circuit and to drive the main motor,
scanner motor, fan, etc.. +3.3VDC is supplied to the sensors and ICs on the engine controller
PCB. +24VDC is divided into +24V, which is normally supplied from the low-voltage power sup-
ply circuit, and +24VR, which is interrupted when the interlock switch (SW1701) is turned OFF
by opening the top cover. This +24VR is supplied to the high-voltage power supply circuit on
the engine controller.
(/DOPEN). The CPU detects the door open with this signal.
Low-voltage power supply circuit
Fuse
Power switch
(FU201) (SW201)
Rectification
Noise
smoothing
filter

circuit

2. Protective functions
The +24VDC power supply circuit and +3.3VDC power supply circuit each have the overcur-
rent/overvoltage protective function, which interrupts the output voltage when troubles such as
short-circuit on the load side cause an excessive current flow or generate abnormal voltage, to
protect the power supply circuit.
If the overcurrent/overvoltage protective function is activated and no DC voltage is output
from the low-voltage power supply circuit, turn OFF the power switch, rectify the problem in the
faulty load, and then turn the power switch ON again.
The circuit has two fuses which break and cut off the power supply if overcurrent flows
through the AC line.
2 - 14
The +24VR also functions as the DOOR OPEN DETECTION signal
Engine controller PCB
Fixing control
circuit
ACH
Noise
filter
ACN
Trans-
former
Fuse
(FU201)
(T601)
Switching
FET (Q601)
Constant voltage
control photocoupler
(PC602)
Control IC
(IC601)
Error state latch
photocoupler
(PC601)
High-voltage power
supply circuit
Figure 2-2-7
Intermediate PCB
+5V
+5V generation
circuit
Rectification
+24V
smoothing
circuit
Rectification
+3.3V
smoothing
circuit
Constant
voltage
control
circuit
Protective
circuit
CPU
/DOPEN
+24VR
Main motor
Laser/scanner
unit
Interlock switch
Video controller
Solenoids
Paper feeder