Toshiba 4560, Service Manual

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Nov. 1997 © TOSHIBA 7 - 13 4560/4570 OPTICAL
The exposure control circuit has the following two functions:
A Manual exposure mode .................. A constant lamp voltage corresponding to the set exposure
step on the exposure lamp is applied.
B Automatic exposure mode ............. The quantity of light reflected by the surface of the original,
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.
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.
170/85 V approx.
76/38 V approx.
190/95 V approx.
[Characteristic curve of the lamp regulator]
PWM pulse duty ratio [%]
Lamp voltage
Range of actual use
Range of actual use
200 V series
100 V series
Limiter voltage
40 % 90 %