| 摘要 |
<p>PURPOSE:To reduce connecting positions, to improve reliability and to decrease its cost by providing a light emitting element, a photodetector connected in series with the element, and a resistor connected in parallel with the photodetector. CONSTITUTION:Since a current from a light emitting diode 11 flows in series with a resistor 15 and a resistor 22 in a state that a light from the diode 11 docs not enter a photo-transistor 12, it becomes relatively small, and the voltage V1 of a terminal A becomes V1=[(V00-VF)/(R15+R22)]XR22, where VCC is the voltage of a DC power source 21, VF is the forward drop voltage of the diode 11, R15 is the resistance value of the resistor 15, and R22 is the resistance value of the resistor R22. When the light of the diode 11 enters the phototransistor 12, the phototransistor 12 can be sufficiently saturated by suitably selecting the resistance values of the resistors 15, 22. The voltage V2 of the terminal A in this case becomes V2=VCC-VF-Fsat, where Fsat is the collector-emitter saturated voltage of the phototransistor 12.</p> |
