Epson LQ-2550 Technical Manual page 73

REV.-A
Figure 2-18 shows a block diagram of the power supply circuit.
External noise on the AC input line is first attenuated by the input filter circuit. Then the input AC is -""
rectified by the full-wave rectifier circuit and smoothed by the smoothing circuit.
Surge current that flows when the printer power is first turned on is suppressed by the surge-
suppression circuit.
The voltage output from the smoothing circuit is converted to various voltages for the control circuits
(+5 V and Y 12 V) and drive circuits (+35 V).
When main switching circuit 1 is activated, voltage is induced in the secondary side of transformer
into + 5 V and * 12 V.
After being rectified and smoothed, the + 5 V output is fed back to main switching circuit 1 by the current
limiting and voltage regulator circuits via the photo coupler, and stabilized.
When the power supply for the control circuits starts operating normally, voltage is induced in the
secondary side of transformer T2. Upon receiving this voltage, main switching circuit 2 turns on, and
voltage is induced in the secondary side of transformer T3. After being rectified and smoothed, the
+35 V output is fed back to main switching circuit 2 by the current limiting, voltage regulator, and .
over voltage protection circuits, and is stabilized.
Power SW.
PRIMARY SIDE TI SECONDARY SIDE
I
1
MAIN SWITCHING
CIRCUIT 1
PRIMARY SIDE T2 SECONDARY SIDE
PRIMARY SIDE T3 SECONDARY SIDE
MAIN SWITCHING
CIRCUIT 2
FULL-WAVE
INPUT FILTER
RECTIFIER
CIRCUIT
m m
RECTIFIER AND
SMOOTHING
CIRCUIT
RECTIFIER AND
SMOOTHING
CIRCUIT
—
-
RECTIFIER AND
SMOOTHING
CIRCUIT
Figure 2-18. ROPS/ROPSE Board Block Diagram
SURGE-SUPPRESSION
CIRCUIT
r
CURRENT LIMITING
AND VOLTAGE
— REGUIATOR CIRCUITS
CURRENT LIMITING
AND VOLTAGE
- REGULATOR CIRCUITS
2-26
SMOOTHING
CIRCUIT
-
ANALOG
AND LOGIC
+5 CIRCUITS
OVER VOLTAGE
PROTECTION
CIRCUIT
MECHANISM
DRIVE