| 摘要 |
PURPOSE:To automatically obtain optimum exposure by electronically controlling the quantity of light of an exposure lamp in accordance with the temp. in a copying machine. CONSTITUTION:When the temp. in the copying machine rises, a thermistor TH decreases its resistance value, and therefore the reference voltage to be applied to the noninversion input terminal of an operational amplifier 64 in a photodetecting circuit 36 rises. Hence, the voltage to be applied to a connection point O4 rises, and the gate voltage of a programmable unijunction transistor PUT53 rises as well, thereby resulting in the decreased conduction angle of a thyristor 32 and the decreased quantity of light of a fluorescent lamp 2. On the other hand, when the temp. in the copying machine lowers, the conduction angle of the thyristor 32 increases and the quantity of light of the lamp 2 increases. |
