Power Supply Circuit Operation - Epson LX-300 Service Manual

2.2.2 Power Supply Circuit Operation

Figure 2-11 shows a block diagram of the power supply circuitry. When AC power is supplied to
the printer from an external power source, a filter circuit removes the noise. l%e AC voltage then
undergoes full-wave rectification and is smoothed to produce the direct current supply voltage.
This voltage is fed through a switching circuit and secondary smoothing circuit to produce the
stepped down +35 VDC supply. A +35V line voltage detector (ZD51 and PCl) circuit is connected
to the switching arcuit. This feedback control arrangement ensures that the +35 VDC supply is
kept stabilized.
A +9 VDC supply is created by putting the +35 VDC line through the +9 VDC power supply
circuit. This arcuit further steps down the +35 VDC voltage and outputs a stabilized supply. The
+9 VDC output is stabilized to +5 VDC using the regulator on the C130 MAIN board assembly.
There are several arcuits to protect the supply arcuits and avoid danger.
The +9 VDC line contains a voltage overload protection circuit. The +9V voltage overload
protection circuit (ZD53, Q82, and PC1) cuts the supply if the voltage reaches or exceeds +11 VDC.
It stops switching circuit operation, which stops the output from the +35 VDC line.
protection circuit ( ZD52, Q82, and PC1 ) cuts the supply if the voltage reaches or exceeds +36 VDC.
It stops switching circuit operation, which stops the output from the +35 VDC line.
Full-Wave
Smoothing
Rectification —
Circuit
Circuit
Filter Circuit
AC Line
Switching Smoothing
Circuit
circuit
A
+9
over-voltage
Circuit
—
Protection
Operating Principk
o +35 VDC (VP)
2-11