Toshiba 4560, Service Manual

Page: 314 / 369

4560/4570 RADF 18 - 56 Nov. 1997 © TOSHIBA
18.11.4 Rush current limitation circuit
This circuit is for suppressing rush current, that flows to current regeneration capacitor C23 included in
the driver motor drive circuit, to a fixed value. This circuit comprises a limiting resistor and FET Q5 that
causes current to flow at steady operation.
During the times that the ZD2 cathode reaches 16 V from when the ADF open/close switch, feed cover
switch and exit cover switch close, base current is not supplied to Q3 causing the circuit to become OFF,
and IC11 pin 5 becomes H-level. At this time, as base current is not supplied to Q2 and the circuit is OFF,
Q5 becomes OFF and the current flows through R37.
On the other hand, when the cathode of ZD2 exceeds 16 V, base current flows to Q3, and the circuit
becomes ON. After a delay according to the time constant of R2 and C35, IC11 pin 5 becomes L-level.
For this reason, base current is supplied to Q2, the circuit becomes ON and Q5 becomes ON. As a result,
the current that had been flowing to R37 up till now, flows through Q5, and the current limitation is
released.
R38 is a discharging resistor for immediately withdrawing the loaded accumulated to C23 when the ADF
open/close switch, feed cover switch and exit cover switch become open.