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THEORY OF OPERATION
3. Power Supply Unit
Fig. 2-17 shows the power supply unit.
The AC power is stepped down to Vs1 and Vs2 by the power transformer. The Vs1 power is full-wave rectified by the
DB1 rectifier stack and smoothed by electrolytic capacitor C4. The smoothed DC power is converted into the stable
25VDC power by the chopper circuit, whose main component is IC1. The Vs2 power is full-wave rectified by the DB2
rectifier stack and smoothed by the electrolytic capacitor C10. Part of this smoothed Vs2 output is converted into the stable
5VDC power by fixed voltage IC2.
Voltage Range Circuit Type Use
Vs1 About 30VAC To 25VDC
Vs2 About 9VAC To 5VDC
25VDC +25V±5% Chopper For print head, carriage motor, paper feed motor
5VDC +5V±2.5% Dropper For IC 5V power, motor holding bias
Fig. 2-17 Power Supply Board
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