Epson Stylus Color 660 Service Manual page 96

EPSON Stylus Color 440/640/740
1) Regardless of the state of power switch (On or OFF), the voltage is
always applied in the primary side of the power supply board from
the moment or at the state that AC-plug is plugged in. At this time,
F1 plays a role of preventing AC100V from coming into the F1. L1
and R1-R2 also prevent high harmonic wave noise generated in the
RC circuit filter which consist of C1∼C4 and R1∼R2 from going out,
and eliminate the noise from outside here.
2) The AC is full-wave rectified by diode bridge DB1, and converted to
x AC in voltage by smoothing electrolytic capacitor C11.
2
3) The pressured up direct current makes Q1 On through the starting
resistor R31 and starts the primary side of the circuit.
4) When the primary side is On state, the energy(current) led by the
electromagnetic induction through the trans (T1) does not flow to the
secondary side since the diode(D51) on the secondary side is
installed in the opposite direction.
5) When the energy which is charged in the trans is reaching the
saturated state, the voltage which makes the Q1 On becomes weak
gradually. At the point that this voltage drops at the certain voltage,
C13 absorbs the current in the opposite direction and Q1 is quickly
shut off by the resulting sharp drop.
6) When the primary side is turned off, the energy charged in the T1 is
opened according to the diode(D51) direction which is installed on
the secondary side. Basically, 42 V DC is output by these circuit
operations and the number of T1 spiral coil.
7) +5VDC is generated by pressured down this +42VDC as power
supply. IC51 pressures down the +42VDC and generates precise
+5VDC by chopping off the output, forming the standard santooth
wave form by the outer RC integration circuit.
Chapter 2 Operating Principles
The C206 PSB/PSE board has various control circuits to stop output if
malfunction on the power supply board, on the main board or on the
duty of printer mechanism happen. Following explains each control and
protection circuits.


+42V Line Constant Voltage Control Circuit:
The output level of the +42V line is monitored by a detection circuit
consisting of seven Zener diodes. This circuit prevents voltage from
dropping for constant output voltage.


+5V Line Over voltage Protection Circuit:
This protection circuit is in the same line as +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 circuit
operation forcefully when the voltage level exceeds +9V.


+42VDC Line Drop Limitation Circuit:
This protection circuit is in the same line as +42V over voltage
protection circuit is located. The output voltage level of the +42V line
is monitored by a Zener diode. This circuit shuts down the circuit
operation forcefully when the voltage level drops +36V.


+42VDC Line Over voltage Circuit:
This circuit is in the same line as +5V line over voltage protection
circuit is located. The output level is monitored by two Zener diodes.
If the voltage level exceeds +48VDC, this circuit stops circuit
operation forcefully.


+5V Line Constant Voltage/Constant Current Control Circuit:
The output current is monitored by a +5VDC generation switching
control IC(IC51), which also monitors the output voltage. This
information is input to the internal comparator and stabilizes +5V
line. Operation of the secondary side switch is explained in the
following page.
Revision A
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