Epson Stylus COLOR 670 Service Manual page 44

EPSON Stylus COLOR 670
Figure 2-12. C301PSB/PSE Board Block Diagram
The C301PSB/PSE board has the various control circuits to stop voltage
output if a malfunction occurs on the power supply board or the main board
while the printer mechanism is on duty. Following explains each control and
protection circuit.
o
+42V line constant voltage control circuit:
The output level of +42V line is monitored by a detection circuit
composed of the seven Zener diodes. When the output voltage
becomes less than 35V, this circuit prevents the voltage from
dropping by driving the primary circuit switching FET.
Operating Principles
o
+5V line constant voltage control circuit:
The output level of the +5VDC line voltage is monitored by the
regulator IC51. If abnormal voltage is detected, the information is fed
back to the internal comparator.
o
+42VDC line over voltage protection circuit:
The output voltage line is monitored by two Zener diodes. If the
output level of the voltage level of +42VDC line exceeds +48V, this
circuit halts the operation of the switching FET and prevents high
voltage from applied to the secondary side.
o
+5V line over voltage/ line over current 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. This circuit shuts down the +5V line
forcefully when the voltage level exceeds +9V.
o
+42VDC line over current protection circuit:
The output voltage is monitored by two transistors. When the output
voltage is dropped abnormally, this circuit regards this as short circuit
and halts the operation of the primary switching FET via photocoupler
to prevent over current from flowing.
Electrical Circuit Operating Principles
Revision A
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