Kyocera Mita DC-2560 Service Manual page 109

1AH
c. Switching control/overcurrent detection circuit
C101
+
Figure 2-3-4 Switching control/overcurrent detection circuit
Switching control IC (IC2) in the switching control circuit emits a pulse signal to FET
(Q102). Current flowing from the active filter circuit to the primary side of the transformer
(TRNS) is switched, generating an e.m.f. at the secondary side. The switching control
IC (IC2) changes the duty cycle of the pulse signal that turns FET (Q102) on and off in
order to control the secondary side output of the transformer (TRNS). The longer FET
(Q102) are on (pulse width), the secondary side output increase; and the shorter the
time during which the FET (Q102) are on, the output voltage decrease. The magnitude
of the secondary output or the pulse width is controlled by the fluctuations in the analog
voltage signal isolated from the error detection circuit by the photocoupler (PC1) and fed
back for pulse width control.
In the overcurrent detection circuit, switching control IC detects the state of the output
current by monitoring the current flows to the resistor (R118) and shutdown the output
when the overcurrent is detected.
From the overvoltage/overcurrent detection circuit at the side of the output circuit,
overvoltage of each DC output and 5 V DC output overcurrent information via
photocoupler conveyed, switching control IC shutdown the output when DC output is
detected overvoltage or overcurrent.
2-3-4
C102
R111
R108
R118
Switching control IC (IC2)
PC2
R112
R113
D105
C103
Q102
C104
R109
PC1
TRNS