Epson Stylus Color, Service Manual

Page: 56 / 151

Chapter2 Operating Principles
Rev. A
2-19
The operating principles of various circuit and controller circuit in the figure above are described below.
+5V Line Over Voltage Protection Circuit:
The output voltage level of +5V is monitored by a Zener diode(ZD53) on the secondary circuit. If the
voltage level exceeds 9V, the Switching FET Q1 goes off by the following operation, and no induced
electromotive force is generated, and generation of +5V and +42V stops as the result.
Zener diode(ZD53) detects the voltage which e9V at the +5V line.
Transistor Q81 goes On.
Photo coupler PC1 goes On.
FETQ31 goes On and the gate voltage for Switching FETQ1 is cut off.
Switching FETQ1 goes Off.
+5V Line Constant voltage Control Circuit:
Voltage at the +5VDC line is monitored by the regulator IC51. Abnormal voltage at the +5VDC line is
detected and the information is fed back to the +5V comparator in the IC, then +5VDC is cut off.
+42V Line Over Voltage Protection Circuit:
The output level of the +42V line is monitored by the 2 Zener diodes;ZD52 and ZD87.
When the output level of the +42V line e48V, the Switching FET Q1 goes Off by the
following operations.
Zener diodes(ZD52, ZD87) detect the voltage which e48V at the +42V line.
Transistor Q81 goes On.
Photo coupler PC1 goes On.
FET Q31 goes On and the gate voltage for switching FET Q1 is cut off.
Switching FET Q1 goes off.
+42V Line Control Circuit:
The output level of the +42V is detected by the Zener diodes; ZD51, ZD81 to ZD86.
When the voltage at the +42V line e38V, the Switching FET Q1 is controlled by the
following operations.
Zener diodes(ZD51 and ZD81 to ZD86) detect the voltage over +38V at the +42V line.
Photo coupler PC1 goes On.
Transistor Q3, Q2 go On and gate voltage for the Switching FET Q1 is cut off.
When the voltage level drops under +38V at the +42 line, the photo coupler PC1 and transistors
Q3 and Q2 go Off and the Switching FET Q1 goes back On.
+42V Line Over Current Protection Circuit:
The output current is monitored by the transistors Q81 and Q82. When the output current is
abnormally low, the information is fed back to the primary circuit via the photo coupler PC1 to
stop the switching operation.
+42V
+5V
AC Input
Filter Circuit
Full Wave
Rectifier Circuit
Smoothing Circuit
Switching Circuit
Photo coupler
Photo coupler
Smoothing Circuit
Primary Side
Secondary Side
+5V Switching Regulator
+5V Constant Voltage Control Circuit
+5V Over Current Protection Circuit
+42V Constant
Voltage Control
Circuit
+5V Over Voltage
Protection Circuit
+42V Over Voltage
Protection Circuit
+42V Over Current
Protection Circuit
Power OFF
Delay Circuit
Power SW
Figure 2-18. C206 PSB/PSE Board Block Diagram