Epson STYLUS 4001968 Service Manual page 37

STYLUS 800 Service Manual
The figure below shows a block diagram of the power supply circuit (C106 PSB/PSE). This power
supply circuit employs the RCC (ringing choke converter) switching control system. The input AC
voltage supplied from the external AC source is first input to the filter circuit for higher harmonics
absorption. The AC voltage is then input to the rectification and smoothing circuit, converting it
into DC voltage. This DC voltage is input to the switching circuit for switching operation. Along
with the switching operation on the primary side, +35 VDC is generated after passing through the
smoothing circuit. The +35 VDC level is fed back to the primary switching circuit through the +35
V line voltage detection circuit and, thus, the +35 VDC output level is stabilized. This +35 VDC is
also input to the +5 VDC generation circuit to generate a stable +5 VDC.
Primary-side
C7
Main
Smoothing
Switching I--Id
Circuit
Full-wave
Rectifier
Circuit
Filter
Circuit
AC Input
Figure 2-12. Power Supply Circuit Block Diagram
This circuit contains the protection circuits described below.
1) +5 VDC line over voltage protection circuit
The output voltage level of +5 V line is monitored with a Zener diode (ZD53) and if the voltage
level exceeds predefined level (+7 V), the status is fed back to the primary switching circuit
through a photocoupler (PC1) to stop the +35 V generation.
+5 VDC line over current protection circuit
2)
The output current is monitored with a detection resistor (R53) and fed back to the +5 VDC
generation switching control IC (IC51). If the current level exceeds the limit, the control IC
shortens the ON
time
(constant current operation).
+35 VDC line over voltage protection circuit
3)
The output level is monitored with a Zener diode (ZD36). If the voltage level exceeds the limit
level (+36 V), it activates a photocoupler (PC1), and this stops the primary switching circuit
operation.
+35 VDC line constant voltage output control circuit
4)
The output level of +35 VDC line is monitored by a detection circuit that consists of a Zener
diode (ZD51), a transistor (Q52), and resistors (R70, R71, R72). This circuit feeds back the
output voltage level status through a photocoupler to the primary switching circuit to control
the ON/OFF time
of
Rev. A
Secondary-side
T1
,.—.
. — ,
Constant
—
Voltage Control -
Pcl !–
of the switching transistor (Q51) to decrease the output voltage level
the switching transistor for constant output voltage control.
I
. .
Operating Principles
Over-current
Protection
. .
2-11