Converting circuit having first and second optically coupled phototransistors and first and second operational amplifiers

Claim 1

A converting circuit comprising: (a) a first terminal; (b) a first transistor whose conduction is controlled on the basis of the voltage applied to said first terminal; (c) a first negative power supply line; (d) a first resistor connected between the emitter of said first transistor and said first negative power supply line; (e) a first positive power supply line; (f) a first light-emitting diode whose anode is connected to said first positive power supply line and whose cathode is connected to the collector of said first transistor; (g) a first phototransistor which is optically coupled to said first light-emitting diode and obtains a current corresponding to the optical signal generated by said first light-emitting diode; (h) a second positive power supply line connected to the collector of said first phototransistor; (i) a second negative power supply line; (j) a second resistor connected between the emitter of said first phototransistor and said second negative power supply line; (k) a second terminal; (l) a load element connected between said second terminal and said second negative power supply line; (m) a second transistor whose conduction is controlled on the basis of the potential of the connection between said first photo transistor and said second resistor and whose emitter is connected to said second terminal; (n) a second light-emitting diode whose anode is connected to said second positive power supply line and cathode is connected to the collector of said second transistor; (o) a second phototransistor which is optically coupled to said second light-emitting diode, and shows collector is connected to said first terminal and emitter is connected to said first negative power supply line; (p) a first operational amplifier whose noninverted input terminal is connected to said first terminal, inverted input terminal is connected to the emitter of said first transistor, and output terminal is connected to the base of said first transistor; and (q) a second operational amplifier whose noninverted input terminal is connected to the connection between said first phototransistor and said second resistor, inverted input terminal is connected to the emitter of said second transistor, and output terminal is connected to the base of said second transistor.