Epson Stylus 1500 Service Manual page 58

The figure below is a block diagram of the power supply circuit (C172 PSB/PSE). The power switch
is in the secondary circuit, allowing the CPU to stay active for a minimum of 20 seconds after the
printer is turned off. This lets the printhead return to the capping position. The CPU 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. AC voltage is first
input to the filter circuit for higher harmonics absorption and then input to the rectification and
smoothing circuit, converting it to DC voltage. The 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 input
to the +5 VDC generation circuit to produce a stable +5 VDC.
Primary
Full Wave
Rectifier
Circuit
Filter
Fuse
AC Input
Figure 2-19. Power Supply Circuit Diagram
+5 VDC Line Over-voltage Protection Circuit
The +5 V line output voltage level is monitored by 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 power is turned on again.
+5 VDC Line Over-current / Over-voltage Control Circuit
The output current is monitored by IC51, a +5 VDC generation switching control IC, which also
monitors the output voltage. This information is input to the internal comparator, causing the
printer to cut the +5 VDC when voltage or current becomes abnormal.
+42 VDC Line Over-voltage 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 +42 VDC line output is monitored by a detection circuit containing Zener diodes ZD51 and
ZD81 to ZD86. This circuit feeds back output voltage level status through photocoupler PC1 to the
primary switching circuit to control switching transistor on/off time for constant output voltage.
+42 VDC Line Overcurrent Protection Circuit
The output current is monitored by transistors Q81 and Q82. This circuit feeds back output voltage
level status through photocoupler PC1 to the primary switching circuit to stop circuit operation.
EPSON Stylus 1500 Service Manual
Main Smoothing
Smoothing
Switching
Circuit
Cricuit
Circuit
Photo-coupler
+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
Operating Principles
Sec ondar y
+42 V
Regulator IC
+5 V
Power Switch
on C172 PNL
2-17