An optically controllable negative resistance circuit constructed with optocouplers

An optocoupler with a Darlington configuration at the output side can be used as a one port active device with a current-controlled negative resistance by simply connecting the input and output sides in cascade. The author proposes an optically controllable negative-resistance circuit constructed with optocouplers. The breakover voltage and the holding current of the negative-resistance characteristics can be controlled widely with two external light inputs. Hence, the circuit may be applied to optronic functional switching operations. It is demonstrated that an optically controlled relaxation oscillator can be easily constructed using the circuit, and that applications of the relaxation oscillator to a light modulator and an optical Schmitt trigger can be realized by simple circuit configurations.