Oki OKIFAX 5400 Maintenance Manual page 310

5-3-3 +5 V circuit
1) +5 V circuit provides +5 V output by lowering +30 V output by means of DC-DC
concerter circuit.
2) IC1 is a control IC of frequency fixed type (operating at about 30 kHz in present power
supply unit)
3) Q1 is a power transistor, D7 is a flywheel diode, and L3 , C10 and C20 compose a
smoothing circuit.
4) The +5 V output is regulated as follows. The rectified +5 V is divided by resistors R83,
R10 and R11 and the resulting voltage is applied to IC1, in which this voltage is
regulated to a constant voltage. Thus, the regulated +5 V output is obtained by
controlling IC1.
5-4 Protection circuits
1) The protection circuit includes fuse F3 for +30 V and +5 V overcurrent protection
circuit.
2) If an overvoltage is applied to the +5 V circuit, D8, R9 and D6 operate to shortcircuit
the +30 V circuit for half-wave cycle and fuse F3 will blow.
3) F1 will blow only in the event of AC line shortcircuit.
5-5 Cover open circuit
1) The cover open circuit consists of SW2. When the stacker cover is opened, the cover
open microswitch (SW2) on the 1VP/2VP board is turned off to cut the supply of H5V
to the high-voltage power supply circuit. As a result all high-voltage outputs are
interruptted. At the same time, the CVOPN-N signal is sent to the control board to notify
it the off state of the microswitch, and the control board performs the cover open
processing.
40838301TH Rev.1 A3 - 29
PWU