Figure 2-19. Power Supply Circuit Diagram - Epson Stylus 1500 Service Manual

Stylus 1500 Service Manual
The figure below shows a block diagram of the power supply circuit (C172 PSB/PSE). The power
switch is in a secondary circuit that allows the CPU to remain active for a minimum of 20 seconds after
the printer is turned off. This allows the printhead to return to the capping position. The CPU, which
is mounted on the C172 MAIN Board, monitors the PSC (power on/off) signal. If this signal goes
LOW, the CPU resets each device after performing the head-capping sequence.
This board also employs an RCC (Ringing Choke Converter) switching system. The AC voltage is first
input to the filter circuit for higher harmonics absorption and is then input to the rectification and
smoothing circuit, converting it into DC voltage. This DC voltage is input to the switching circuit.
Along with the switching operation on the primary side, +42 VDC is generated after passing through
the +42 V line voltage detection circuit. This +42 VDC output level is stabilized and is also input to the
+5 VDC generation circuit to produce a stable +5 VDC.
Full Wave
Rectifier
Circuit

Figure 2-19. Power Supply Circuit Diagram

+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 photocoupler PC1 to cut the +42 V until
the power is turned on again.
+5 VDC Line Overcurrent / Overvoltage Control Circuit
The output current is monitored by a +5 VDC generation switching control IC (IC51), which also monitors
the output voltage. This information is input to the internal comparator and cuts the +5 VDC when the
voltage or current becomes abnormal.
+42 VDC Line Overvoltage Protection Circuit
The output level is monitored by two Zener diodes (ZD52 and ZD87). If the voltage level exceeds +48 V,
photocoupler PC1 is activated to stop the primary switching circuit operation.
+42 VDC Line Drop Protection Circuit
The output level of the +42 VDC line is monitored by a detection circuit consisting of Zener diodes (ZD51
and ZD81 to ZD86). This circuit feeds back the output voltage level status through photocoupler PC1 to the
primary switching circuit, to control the on/off time of the switching transistor for constant output voltage.
+42 VDC Line Overcurrent Protection Circuit
The output current is monitored by transistors Q81 and Q82. This circuit feeds back the output voltage level
status through photocoupler PC1 to the primary switching circuit to stop the circuit's operation.
Rev. A
Primary
Main
Smoothing
Switching
Cricuit
Circuit
Filter
Photo-coupler
Fuse
AC Input
Sec ondar y
Smoothing
Circuit +42 V
Regulator IC
+5 V
+42 V Line Drop
Protection Circuit
+42 V Line Over
Current Protection
Circuit
+42 VDC Line Over
Voltage Protection
Circuit
+5 VDC Line Over
Voltage Protection
Circuit
Power off Detection
/ Delay Circuit
Power Switch
on C172 PNL
Operating Principles
2-15