Epson L-1000 Technical Manual page 75

PRINCIPLES OF OPERATION
Constant Current Drive Circuit
The carriage motor-drive current is given by the following equation:
I = VrCD/R79 = VrCD/1.2 ohms
When the carriage stops, port PB5 of the CPU is set HIGH, the input to the chopping circuit becomes 0 V,
and current is applied from the + 5 V line to the motor via resistor R1 and diode D1. This current is given by:
(5 V - VD15 - VD5)
I =
R76 - 21 ohms/phase + R79
Figure 2-38 shows the constant current circuit; Table 2-6 lists the current values for reference voltages.
2-38
Figure 2-38. Constant Current Control Circuit
REV.-A
LQ-500 / L-1000