The figure below shows a block diagram of the power supply circuit (C137 PSB/PSE). The power
switch is equipped with a secondary circuit that allows the CPU to remain active for a while after
the printer is turned off. This allows the printhead to return to the capping position after power is
off. The CPU mounted on the C137 MAIN Board always monitors the PSC (power on/off) signal. If
thissignal becom es LOW, the CPU resets each device after performing the head capping sequence.
Also, this board employs the RCC (ringing choke converter) switching system. This AC voltage is
first input to the filter circuit for higher harmonics absorption, and then input to the rectification
and smoothing circuit, converting it into DCvoltage. This DC voltage is then input to the switching
circuit for the switching operation. Along with the switching operation on the primary side, +35
VDC is generated after passing through the +35 V line voltage detection circuit. This +35 VDC
output level is stabilized. This +35 VDC is also input to the +5 VDC generation circuit to generate a
stable +5 VDC.
1)+5 VDC line over v oltage protection circuit
The output voltage level of +5 V line is monitored by a Zener diode (ZD53). If the voltage level
exceeds +7 V, the status is fed back to the primary switching circuit through a photocoupler (PC1)
tostop the +35 V generation.
2)+5 VDC lineo ver current / over voltage control circuit.
The output current is monitored by a detection resistor (R53) and fed back to the +5 VDC
generation switching control IC (IC51), which monitors the output voltage. This information is
input to the internal comparater and outputs the high signal to turn off the transistor (Q51) when
thevoltage orthe currentbe comes abnormal.
3)+35 VDC line over voltage protection circuit
The output level is monitored by a Zener diode (ZD36). If the voltage level exceeds +36 V, a
photocoupler(PC1) is activate d; stopping the primary switching circuit operation.
4)+35 VDC line drop prote ction circuit
The output level of +35 VDC line is monitored by a detection circuit that consists of a Zener diode
(ZD51 and ZD81 to 84). This circuit feeds back the output voltage level status through a photo-
coupler to the primary switching circuit to control the ON/OFF time of the switching transistor for
contastoutpu t voltage.
F1
L1, R1 C1-C4
DB1 C11
Q1
T1 C51 +35 VDC
ZD51, 81-84
TL 494
+5 VDC
ZD52
ZD53
PC1
ZD86,
C82
P-OFF Signal
Full-wave
Rectifier Circuit Smoothing
Circuit
Filter Circuit
Fuse
Main Switching
Circuit
Feedback
Circuit
Transformer
Smoothing
Circuit
Drop Protection
Circuit
P-OFF Detection
and Delay Circuit
Over Voltage
Protection Circuit
Photo
Coupler
Over Voltage
Protection Circuit
Figure 2-16. Power Supply Circuit Block Diagram
Operating Principles Stylus Pro XL
2-14 REV.-A