Epson STYLUS COLOR 3000 Service Manual page 55

Operating Principles
Figure 2-14 illustrates the electrical circuit diagram.
Full Wave
Rectifier
Circuit
Filter
Fuse
AC Input
+5 VDC line overvoltage protection circuit
The output voltage level of the +5 V line is monitored by a Zener diode (ZD53). If the voltage level exceeds
+9 V, the status is fed back to the primary switching circuit through the transistor (Q82) and photocoupler
(PC1) to cut off the +42 V line to the regulator (IC51).
+5 VDC line constant voltage control circuit
Voltage at the +5 VDC line is controlled by the regulator IC (IC51). When abnormal voltage at the +5 VDC
line is detected, the status is input to the internal comparator of the regulator, controlling the voltage.
+42 VDC line overvoltage protection circuit
The output level of the +42 VDC line is monitored by the 2 Zener diodes ZD52 and ZD87. When the output
level of the +42 VDC line exceeds +48 V, the switching FET operation on the primary side is stopped via the
thyristor (CY52), transistor (Q81), and photocoupler (PC1).
+42 VDC line constant voltage control circuit
Voltage at the +42 VDC line is monitored by the Zener diodes (ZD51, ZD81−ZD86). This circuit feeds the
output voltage level status through a photocoupler (PC1) to the primary switching circuit to control the
switching FET to produce a constant output voltage level.
+42 VDC line overcurrent protection circuit
Output current is monitored by transistors Q81 and Q82. If the measured output current is abnormally low,
there is a short circuit, and the overprotection circuit has fed back to the primary circuit to stop the switching
FET operation.
2-14
Primary Circuit
Switching
Smoothing
Circuit
Circuit
(Q1)
Figure 2-14. Power Supply Circuit Diagram
Secondary Circuit
Half Wave
Rectifier
Circuit
Chopping
Regulator
(IC51)
Photo-coupler
PC1
+42 V Line Constant
Voltage Control Circuit
(ZD51, 81 to 86)
+42 V Line Overcurrent
Protection Circuit
(Q81, Q82)
+42 V Line Overvoltage
Protection Circuit
(ZD52, ZD87, Q81)
+5 V Overvoltage
Protection Circuit
(ZD53, Q82)
Power Off Delay Circuit
(ZD88, C84, Q84)
EPSON Stylus Color 3000 Service Manual
+42 V
+5 V
Power Off Signal