Epson LQ 300 - Power Supply Circuit Operation

LQ-300 Service Manual
Operating Principle
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
cinmit removes the noise. The 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 +35 V line voltage detector (ZD51 and PC1) circuit is connected
to the switching circuit. 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
cimuit. This circuit 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 circuits to protect the supply arcuits and avoid danger.
The +9 VDC line contains a voltage overload protection circuit. The +9 V voltage overload
protection circuit (ZD53, Q82, and PC1) cuts the supply if the voltage reaches or exceeds +11 VDC.
It stops switching arcuit operation, which stops the output from the +35 VDC line.
The +35 VDC line has a voltage overload protection circuit. The +35 VDC voltage overload
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
Rectification
—
Smoothing
Switching
Smoothing
Circuit
Circuit
Circuit
Circuit
4
T
Filter Circuit
AC Line
-Ez!t
c1
+9 VDC Line
Over-voltage
Protection
Circuit
I +35 VDC Linel
I
— Over-voltage
Protection
t
Figure 2-11. Power Supply Circuit
Circuit
I
Block Diagram
~ +35 VDC (VP)
-+9 VDC (VL)
Rev.A
2-11