Toshiba 4560 Service Manual page 75

The exposure control circuit has the following two functions:
A Manual exposure mode .................. A constant lamp voltage corresponding to the set exposure
B Automatic exposure mode ............. The quantity of light reflected by the surface of the original,
7.5.2 Operation of lamp regulator
A typical characteristic curve is shown in the following diagram.
By means of a phase-angle control system, a lamp voltage corresponding to the PWM pulse duty
ratio input is generated even if some fluctuation occurs in the AC input voltage.
Lamp voltage
190/95 V approx.
170/85 V approx.
76/38 V approx.
100 V series
200 V series
Nov. 1997 © TOSHIBA
step on the exposure lamp is applied.
which varies infinitely with the lightness and darkness of
the surface of the original, is detected by the automatic ex-
posure sensor circuit, and the voltage applied to the expo-
sure lamp is continually varied accordingly; a high lamp
voltage being impressed for dark originals and a low lamp
voltage for light originals.
Range of actual use
40 %
[Characteristic curve of the lamp regulator]
7 - 13
Limiter voltage
90 % PWM pulse duty ratio [%]
4560/4570 OPTICAL