Abstract: In a lateral transistor having a first semiconductor region of one conductivity type, and an emitter region and a collector region both having the opposite conductivity type and disposed in the first semiconductor region; a second semiconductor region having the opposite conductivity type is disposed opposite to the emitter region with respect to the collector region. The thus obtained lateral transistor has a characteristic that a current flowing to the substrate is prevented under a saturation operation state and is suitably used to form, e.g., a current-mirror type constant-current circuit constituting a switching device having improved threshold characteristics.

Abstract: A switching device is constituted by two transistors having different emitter areas, a resistor connected to a transistor having a larger emitter area, a driving transistor having a control electrode connected to the collector of the transistor having a smaller emitter area, and a constant-current circuit connected to the two transistors so as to supply equal currents to the two transistors. The bases of the two transistors are equally biased to a constant level. An input current is supplied to the switching device through an input terminal and is divided into the emitter currents of the two transistors. The relative largeness of the collector currents of the two transistors are reversed when the input current exceeds the threshold, thereby to cause the potential change at the collector of the transistor having a smaller emitter area to operate the driving transistor and to control the current supply to the load.

Abstract: A switching device includes a current supply circuit, a control circuit, and means for feedback from the current supply circuit to the control circuit. The current supply circuit supplies current to a load. The control circuit controls operating and non-operating of the current supply circuit. When the current supply circuit is inoperative, means for feedback renders the control circuit inoperative.