Service manual

Principles of Operation
Table 2-4. Current Values for Reference Voltages
Positive feedback through R9 generates a hysteresis in the comparator of ICl.
The upper limit of the hysteresis is the reference voltage. The comparator works
like a Schmitt trigger, sensing a difference when the inverse terminal feedback is
slightly larger or smaller than the hysteresis level. The comparator in ICl
compares reference voltage a! and the feedback voltage.
When reference voltage (Y is HIGH, TR6 goes on and applies approximately
25 VDC to the coil. The current rises linearly due to inductance. TR6 goes off
when the feedback voltage equals the reference voltage. In this way, an almost
constant current is applied to the coil.
Figure 2-36 shows the carriage motor’s drive current waveform (pin 12) and the
chopping waveform (pin 17) of the drive voltage (+24 v) at 960 pps. Figure 2-37
shows the Schmitt trigger circuit.
Figure 2-36. Chopping Waveforms
LQ200/AP3000
2-37