Power Source Pcb - Kyocera KM-2550 Service Manual

2-3 Operation of the PWBs
2-3-1

Power source PCB

CN1
Power switch
AC
INPUT
F3
L4
DH1.LIVE
DH1.OUT
DH2.LIVE
DH2.OUT
SH.OUT
H.LIVE
MH.OUT
The power source PCB (PSPCB) is a switching regulator that converts an AC input to generate 24 V DC and 5 V DC. It
includes a rectifier circuit, a switching regulator circuit, a 24 V DC output circuit, a 5 V DC output circuit, overvoltage detec-
tion circuit, zero-cross circuit and a fixing heater control circuit.
The rectifier circuit full-wave rectifies the AC input using the diode bridge D1. The smoothing capacitor (C5) smoothes out
the pulsed current from the diode bridge.
In the switching control circuit, switching circuit turns the power MOSFET (Q1) on and off to switch the voltage induced in
the primary coil of the transformer (T1).
The 5 V DC output circuit rectifies and smoothes the voltage induced in the secondary coil of the transformer (T1) via
diodes (D102) and smoothing capacitors (C102, C105), and the output is controlled by the overvoltage detection circuit
(IC101). For 5 V DC output, the switching circuit of the switching control circuit changes the duty of the switching pulse
width of the power MOSFET (Q1) via a photo coupler (PC1) based on the output voltage status to adjust the 5 V DC out-
put.
The 24 V DC output circuit rectifies and smoothes the voltage induced in the secondary coil of the transformer (T1) via
diodes (D101) and smoothing capacitors (C101, C104), and the output is controlled by the overvoltage detection circuit
(IC101).
The zero-cross circuit detects zero-crossing of the AC input voltage with the AC detection circuit and outputs the zero-
cross signal (ZCROSSC) from the zero-cross output circuit through the photo coupler (PC3).
The fixing heater control circuit is divided into the sub-heater output (SH.OUT) and the main heater output (MH.OUT).
When the control signals (SHEATN and MHEATN) input from the machine engine side show a low level, this circuit turns
on the sub-heater and the main heater respectively by turning on the photo triac couplers (PC2 and PC201) with a zero-
cross circuit to turn on the triacs (TRA1 and TR201) in the fixing heater ON/OFF circuit.
The power-saving control circuit performs power-saving control by turning off the 24 V DC output in the 24 V DC output
ON/OFF switching circuit and controlling the switching control circuit and the AC detection circuit through the photo cou-
pler (PC4) to decrease the switching frequency, stop the starting circuit in the switching control circuit, and stop the AC
detection circuit when the sleep signal (SLEPN) input from the machine engine side is low.
In addition, 5 V DC 3-terminal regulator (IC102) is connected to the back of the 24 V DC output ON/OFF switching circuit
to output +5 V1, and this output stops when the sleep signal (SLEPN) is low.
L1
F1
L2
D1
C5
F2
Q1
L3
Switching
control circuit
D33 D30
AC
Zero-cross circuit
detection
circuit
Fixing heater
ON/OFF circuit
(TRA1,TR201)
Fixing heater
control circuit
Figure 2-3-1 Power source PCB block diagram
T1
D101
Q2
C101
C104
D206
Energy
save
control
circuit
C102
C105
Rectifier circuit
D109
D104
PC4
Overvoltage
PC5
detection circuit
PC1
PC3
PC2
PC201
24 V DC
output
Q151
circuit
D111
D110
Energy
5 V DC
save
output
control
circuit
circuit
Q153
IC101
Q154
5 V DC
3-terminal
regulator
(IC301)
Zero-cross
output circuit
2FT
+24V
+24V1
GND
+5V
SLEPN
GND
+24V2
+5V1
ZCROSSC
SHEATN
MHEATN
2-3-1