Oki OKIFAX 5400 Maintenance Manual page 309

PWU
5. General functional description
5-1 General
The power supply unit consists mainly of AC transformer and a power PCB (1VP board for
AC120V/2VP board for AC230V). A block diagram of the power supply unit is shown in Figure
A3.3.1 The power PCB is composed of five main circuits: AC input section, heater control
section, low-voltage section, high-voltage section and protection circuit.
The low-voltage section provides a +5V output by a DC-DC converter and other output
voltages (+30V, +8V and -8V) simply by rectifying and smoothing the respective outputs of
the AC transformer. The high-voltage section (TR1, TR2, DB1, DB2, SB1, SB2, CB and CH)
produces a flyback voltage from 5V by using a drum coil and a high-voltage transformer.
5-2 Circuit description
5-2-1 AC input section
1)
2)
3)
5-2-2 Heater control circuit
1)
2)
3)
5-3 Low-voltage section
5-3-1 +30 V circuit
1)
2)
5-3-2 +/- 8 V circuit
1)
2)
40838301TH Rev.1
AC commercial power is supplied to line filter circuit through the AC inlet, power switch
(SW1) and the fuse (F1). Fuse F1 is used for protecting the heater circuit.
The filter circuit consists of L101,R1, C1, C2, C3 and L1. Capacitors C1 and C2 are
not mounted in the power unit for 120VAC input.
Fuse F2 is used for protection for the double voltage input in the power supply unit for
120VAC input and will not blow by shorting or opening the secondary circuit. This fuse
F2 is not mounted in the power supply unit for 230VAC input.
The AC power divided from the AC input section passes through L2 for noise
elimination and is fed to the heater via D1 (operating as a switch) from the power PCB.
The on/off operation of D1 is controlled by the operation of photocoupler PC1 whose
operation is controlled by the HEAT-N signal applied to CN3-B7 pin from the control
PCB (M17 board).
Resistors R2 and R3 connected on the AC side of PC1 are fuse resistors to protect
themselves from firing when PC1 turns on in the event of D1 open failure.
The +30 V circuit provides +30 V output by rectifying the corresponding output of
transformer T1 by a rectifier diode DS1 and smoothing the rectified signal by capacitor
C7.
Resistor R53 is used to discharge the elecetric charge of C7 when the power switch
(SW1) turned off.
The +/- 8 V circuit provides +8 V and -8 V outputs by rectifying the corresponding output
of transformer T1 by rectifier diodes D10 and D11 and smoothing the rectified signals
by capacitors C13 and C14.
Resistors R22 and R23 are used to discharge the electric charge of C13 and C14 when
the power switch (SW1) is turned off.
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