Toshiba 4580, Service Manual

Page: 101 / 379

Mar. 1999 © TOSHIBA TEC 7 - 11 6570/5570 SCANNER
7.5.4 Lamp regulator circuit
The lamp regulator circuit ensures that illumination from the exposure lamp is constant. Any tendencies
for variances in illumination is monitored and controlled by a series of detection and comparison circuits.
Its principle control is as follows:
(1) AC115V (or 220/240V) power source is rectified to provide DC160V (or 310/340V) which is used as
the power source for the exposure lamp.
(2) The PWM1 signal for light adjustment is averaged by an integration circuit and provides reference
VS for feedback control of the lamp regulator circuit.
(3) When the oscillator circuit is triggered by EXPO-ON/OFF signal, it generates a lamp drive PWM2
signal which turns on the lamp drive transistor (T
r1
), causing current I
1
to flow through:
Capacitor C
→
Exposure lamp (L)
→
Primary side of T1 (P)
→
Lamp drive transistor (T
r1
)
→
Capaci-
tor C
This causes current I2 proportional to the winding ratio of T1 and the rate of change of I
1
to generated
on the secondary side of T1(s).
(4) The amount of lamp current converted to detection voltage VD by a current detection circuit is com-
pared with the smoothing signal VS of PWM1 signal from the logic circuit by a comparison circuit
whose difference signal VF is fed back to the oscillator circuit.