Kyocera Mita KM-4530 Service Manual page 337

2BC/D
The power source PCB (PSPCB) is a switching regulator which converts an AC input to generate 24 V DC, 5.2 V DC, 3.3 V
DC and 12 V DC. It includes the components shown in Figure 2-3-1; noise filter circuits, a rectifier circuit, a PWM control
circuit, a 24 V DC output circuit, a 5.2 V DC output circuit, a 3.3 V DC output circuit, a 12 V DC output circuit, a fixing heater
control circuit, an overvoltage/overcurrent detection circuit.
The noise filter circuit, consisting mainly of noise filter circuits L1 and L2 in the power source section and capacitors,
attenuates external noise from the AC input and prevents switching noise generated by the power source circuit from
leaving the machine via the AC line. Choke coil L4 prevents the noise generated in the heater circuit when the heater turns
on from leaving the machine via the AC line.
The rectifier circuit full-wave rectifies the AC input which has passed through the noise filter circuits L1 and L2 using the
diode bridge D1.
In the PWM control circuit, PWM controller IC1 turns FETs Q1 and Q2 on and off to convert DC voltage full-wave rectified via
diode bridge D1 and smoothed by electrolytic capacitor C22 to a high-frequency voltage, which is applied to the primary coil
of the transformer.
The 24 V DC output circuit smooths the current induced on the secondary coil of the transformer via diodes D12, D13 and
D14 and smoothing choke coil L6, providing a more stable 24 V DC through 24 V DC control circuit including IC2. It also
monitors the 24 V DC output status, which is fed back to PWM controller IC1 in the PWM control circuit via photocoupler
PC2. PWM controller IC1 controls the switching duty width of switching FETs Q3 and Q4 based on the output voltage status,
producing a stable 24 V DC output.
The 5.2 V DC output circuit receives 24 V DC from the 24 V DC control circuit and outputs a stable 5.2 V DC via DC/DC
converter controller IC3.
The 3.3 V DC output circuit receives 5.2 V DC from the 5.2 V DC control circuit and outputs a stable 3.3 V DC via regulator
IC IC4.
The 12 V DC output circuit receives 24 V DC from the 24 V DC control circuit and outputs a stable 12 V DC via DC/DC
converter controller IC5.
Abnormal rise of voltage for all DC outputs and overcurrent in 5.2 V DC and 12 V DC outputs are monitored by the
overvoltage/overcurrent detection circuit, and if any abnormal rise is detected, alarm signals are fed back to the PWM
control circuit IC1 via photocoupler PC1 instantly, by which means power supply is limited to the stand-by level. Overload of
the 24 V DC output is monitored by resistors R34 and R35 as the total sum of all DC output power. If any abnormal condition
is detected, the power supply is latched off. To recover the power supply, remove the cause of abnormality and turn the AC
input off and back on.
The fixing heater control circuit sends a zero-crossing signal from the zero-crossing circuit via the photocoupler PC3 to the
main PCB (MPCB). These signals are in turn converted into signals to control the on/off timing and phases, which are then
input to the power source PCB (PSPCB) as FH-M REM and FH-S REM signals. The phototriacs PT1 and PT2 are turned on
by these signals, and current flows through triacs TR1 and TR2 to turn the fixing heaters FH-M and FH-S on.
2-3-2