Power Supply Circuit Operation - Epson DFX-8000 Service Manual

Power Supply Circuit Operation

2.2.2
Figure 2-13 shows a block diagram of the power supply circuit.
The basic constructions of the BOPS and BOPSE units are the same. The figures in parentheses are
the current or voltage value, and the lower portions of the rectangles indicate the locations of major
elements.
The AC voltage is input to the AC inlet, and is supplied to the power supply board via the POWER switch
and fuse. The AC voltage is rectified (BOPS: voltage doubler rectifier, BOPSE: full-wave rectifier), then
smoothed by DB 1.
The surge-suppression circuit suppresses the surge current that flows when the printer power is turned
on.
The DC voltage is divided into two lines; +35 V and + 5 V, and is converted into the DC voltages required
to operate the printer by the RCC switching regulator circuits.
+35 V line
The +35 V line performs DC to DC conversion via T1 and DT1.
The current limiter monitors the current input to R32 (total of VP1 to VP3, each current is 4A), and
feeds it back to error amplifier 1 (EA2) in IC 1. The constant voltage controller monitors the voltages
input to R34 and VR 1 (for setting the +35 V line voltage), and feeds it back to IC 1 (EA1 ).
and Q2 via transformers T2 and T3.
off by setting the dead time to 10OYO.
In this circuit, four feedback paths can be used for the DTC.
One is the feedback from the limiter for each output current from VP1 to VP3, which activates the
The current limiter (R32) mentioned above is used to recover this limiter.
The second is the feedback from the current limiter.
The third is the feedback from the power down (PD) signal on the main board. If an error occurs and
it is necessary to cut the voltage to prevent the printer from being damaged, the DTC is activated
by the PD signal.
The forth is the feedback from the ground level monitor, which activates the DTC, and cuts the voltage
to prevent the printer from operating abnormally if the potential difference between the ground (G ND)
levels of the +35 V and +5 V lines cause a current of 1A to flow.
+5 V line
The +5 V line performs DC-DC conversion via T4 and DT2.
The current limiter monitors the current flow to R66 and feeds it back to IC4A (comparator).
The constant voltage controller Q8 (shunt regulator) feeds back the voltage fluctuation to Q5 (~ Q4).
The &12 V line is also output in parallel from the + 5 V line. When the +5 V line becomes stable,
the + 12 V line also becomes stable. In this circuit, fuse resistors R7 1 and R72 work as a current
limiter.
2-17
REV.-A