Power Source Pcb - Kyocera Mita KM-1530 Service Manual

2-3-1 Power source PCB

Power source PCB
D1
AC input
Noise
filter
circuit
C14
Zero-cross
detection circuit
PC1
TR1
Fixing heater control circuit
HEATER COMMON
The power source PCB (PSPCB) is a switching regulator that converts an AC input to generate 24 V DC, 5.1 V DC, 3.3 V DC
and 12 V DC. It includes a noise filter circuit, a rectifier circuit, a switching regulator circuit, a 24 V DC output circuit, a 5 V DC
output circuit, a 3.3 V DC output circuit, a 12 V DC output circuit, a fixing heater control circuit and a phase control circuit.
The noise filter circuit consists mainly of a line filter and capacitors. It reduces external noise from the AC input and prevents
switching noise generated by the power source PCB from leaving the machine.
The rectifier circuit full-wave rectifies the AC input that has passed through the noise filter circuit using the diode bridge D1.
The smoothing capacitor C14 smoothes out the pulsed current from the diode bridge.
In the switching control circuit, PWM controller IC1 turns the power MOSFET Q1 on and off to switch the current induced in
the primary coil of the transformer T1.
The 24 V DC output circuit smoothes the current induced in the secondary coil of the transformer T1 via diode D9 and
smoothing capacitors C29 and C30, and outputs a stable 24 V DC by the function of the shunt regulator IC2. It also monitors
the 24 V DC output status, which is fed back to PWM controller IC1 in the switching control circuit via photocoupler PC2.
PWM controller IC1 controls the switching duty width of the power MOSFET Q1 based on the output voltage status,
producing a stable 24 V DC output.
The 5.1 V DC output circuit consists of a step-down chopper circuit that uses IC4 as the control IC. It outputs a stable 5.1 V
DC.
The 3.3 V DC output circuit converts the 5 V DC from the 5 V DC output circuit to a stable 3.3 V DC by means of the 4-pin
regulator IC5.
The 12 V DC output circuit converts the 24 V DC from the 24 V DC output circuit to a stable 12 V DC by means of the 4-pin
regulator IC3.
The phase control circuit and zero-cross detection circuit prevent flicker problems. These circuits modify the fixing heater on
signal from the main PCB (MPCB) to prevent abrupt variations in current when turning the fixing heaters on and off, and
convey the signal to the fixing heater control circuit.
The fixing heater control circuit is controlled by the fixing heater on signal modified at the phase control circuit. The
phototriac PT1 turns on when the fixing heater on signal goes low. When the phototriac PT1 is turned on, current flows
through the triac TR1 to turn the fixing heaters on.
T1
Rectifier circuit
D9
C29,30
Q1
Switching
regulator
circuit IC1
PC2
PC3
Phase
control
circuit
PT1
5 V DC
Figure 2-3-1 Power source PCB block diagram
24 V DC
output
circuit
IC2
12 V DC
output circuit
IC3
C34
5.1 V DC output
+
C37,91
circuit IC4
3.3 V DC
output circuit
IC5
Overvoltage
detection circuit
2AV/X
24 V DC
GND
12 V DC
C32
GND
5.1 V DC
GND
3.3 V DC
C43
GND
HEATER REM
2-3-1
2-3