| 摘要 |
PURPOSE:To prolong the hold time as soon as an ATC function operating time is shortened by setting variably a threshold voltage even at no signal without any electric signal resulting from a light signal. CONSTITUTION:When a threshold voltage b1 is lower than a voltage at the 2nd input terminal of a comparator 1, in this case, a signal c1, an output of the comparator 1 is not given and then a transistor (TR) 2 is turned off. In this case, although the voltage b1 is nearly maintained, a charging current flows to a capacitor 3 from a constant current source 4, resulting in that the voltage across the capacitor 3 rises gradually. When the voltage b1 is higher than the signal c1, a signal is outputted from the comparator 1 and the TR 2 is turned on. Then a current flows between the collector and emitter of the TR 2, the capacitor 3 is charged negatively and the voltage b1 falls down. When the voltage b1 gets higher than the voltage of the signal c1, the output from the comparator 1 is lost, the TR 2 is turned off and the voltage b1 acts like ATC functions according to the signal c1. |
