Epson Stylus PHOTO 950 Service Manual page 45

EPSON Stylus PHOTO 950
2.3.1.2 Protection Circuit
The C456PSB/PSE board has the various control circuits to stop voltage output if a
malfunction occurs on the power supply board or the main board or while the printer
mechanism is on duty. Following explains each control and protection circuit.
+5V line over voltage protection circuit:
This protection circuit is in the same line as the +42V over voltage protection
circuit is located. The output voltage level of the +5V line is monitored by a Zener
diode.(ZD53) This circuit shuts down the +5V line forcefully when the voltage
level exceeds +7V.
+42VDC line drop limitation circuit:
This protection circuit is in the same line as +42V over voltage protection circuit is
located. The output voltage level of the +42V line is monitored by a Zener
diode.(ZD88) This circuit shuts down the +42V line forcefully when the voltage
level drops to +36V.
+42VDC line over voltage circuit:
This circuit is in the same line as +5V line over voltage protection circuit is
located. The output level is monitored by two Zener diodes.(ZD52, 87) If the
voltage level exceeds +48VDC, this circuit shuts down the +42V line forcefully.
+5V line control circuit:
The output current is monitored by the +5VDC generation switching control IC
(IC51), which also monitors the output voltage. This information is input to the
internal comparator and stabilizes +5V line.
OPERATING PRINCIPLES
2.3.1.3 PS Control Function
The power supply circuit is equipped with a secondary power supply, so that even if
the power is turned off by means of the power switch on the control panel, voltages can
still be supplied to the 5V line and to the 42V line for approximately 30 seconds. As a
result, the following operations are carried out even if the power switch is turned off
while the printer is operating.
If the printer is in the process of printing and the CR unit is not at the home
position, the CR unit finishes printing and returns to the home position. Once
the carriage has been locked, the power turns off.
Even if the printer is not currently in the process of printing but paper has
been fed from the ASF and is still inside the printer mechanism, the paper is
ejected and then the power is turned off.
2.3.1.4 Energy Save Mode
The power supply circuit switches to energy saving mode in response to the ESAVE
signal from the control circuit. When the power supply circuit is in energy save mode,
the +42V line repeatedly rises and falls within a lower limit of 20V and an upper limit
of 23V.
Electrical Circuit Operating Principles
Revision A
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