Protection Circuits; Power Supply Control Function; Energy Save Mode - Epson Stylus PHOTO 890 Service Manual

EPSON Stylus Photo 890/1280/1290

2.2.1.2 Protection Circuits

The C378PSB/PSE board has the various protection circuits to stop voltage outputs if
an abnormal condition relating to the control circuit or the printer mechanism's duty
occurs.
o
+42VDC Line Constant Voltage Control Circuit:
The output level of the +42V line is monitored by a detection circuit composed of
numbers of Zener diodes, and the information is fed back to the primary side via
photo coupler PC1. Along with the fed back signal, the switching FET on the
primary side varies the level of the voltage output to the secondary side by
changing its frequency to keep the voltage up.
o
+42VDC line over current protection circuit:
If the +42 VDC line is over currented, the output voltage level drops drastically.
When the voltage level is 36V or lower, zener diode ZD90 detects that condition
and sends information to the primary side via photo coupler PC1. In the primary
circuit, then, switching operation stops to protect the electrical circuits and printer
mechanism. To reset the circuit, turn the printer off and back on.
o
+42VDC line over voltage protection circuit:
If the voltage level of the +42VDC line exceeds 59V, zener diodes D52 and ZD87
detect it and feed back the information to the primary side via photo coupler PC1.
The switching operation in the primary side then stops to protect the electrical
circuits and printer mechanism.
o
+5V line constant voltage/constant current control circuit:
Both +5V line output voltage and +5V line output current are monitored by
chopper IC (IC51). Detected information is input to the IC's internal comparator
and stabilizing circuit. When the IC detects abnormally high current level, it stops
outputting voltage. The circuit recovers automatically.
o
+5V line over voltage protection circuit:
If the +5VDC output level exceeds 12V, zener diode ZD53 detects that condition
and feeds back the information to the primary side via photo coupler PC1. The
switching operation in the primary side then stops to protect the electrical circuits
and printer mechanism.
OPERATING PRINCIPLES

2.2.1.3 Power Supply Control Function

Since this printer has the power switch in the secondary circuit, even if its power is
turned off through the operation panel, it can continue to supply voltage to the +5VDC
line and +42VDC line for about 30 seconds. This extra time allows the printer to
complete the following operations:
o
If the printer is in a printing motion and the CR unit is out of its home position, the
printer stops printing, returns the CR unit to the home position, and performs CR
lock operation. Then the printer power shuts down.
o
If the printer is not printing but paper loaded at ASF remains in the printer, the
printer ejects the paper before the printer power shuts down.

2.2.1.4 Energy Save Mode

The power supply circuit enters the energy save mode by the signal ESAVE sent from
the control circuit. One the circuit is in this mode, it maintains the +42V line level in a
range from +20V to +23V.
Electrical Circuit Operating Principles
Revision C
46