Abstract: There is disclosed a two wire AC power supply for proximity switch integrated circuits. A problem has existed with previous power supplies in that such have been implemented using discrete devices, which take up valuable room on any printed wiring assembly. This invention therefore provides a two wire AC power supply for a proximity switch integrated circuit, wherein at least some circuitry associated with the power supply is provided within the integrated circuit. The power supply preferably comprises a bridge rectifier (BR1), a voltage regulator (Z1, R1, M1), a thyristor (SCR), a diode (D1), a storage capacitor (CVS), a comparator, and an AND gate, wherein at least the comparator and the AND gate are provided within the integrated circuit.

Abstract: A proximity switch circuit including first and second transistors Q4, Q6 connected as a long tail pair with an inductive sensing circuit LC connected to one leg thereof and an emitter follower circuit Q7, Q8 connected between said one leg and the base of the transistor of the other leg, whereby an oscillator circuit can be provided which is non-critically damped to enable faster speed of operation of the proximity switch.

Abstract: The present invention provides an integrator 5 with switched hysteresis for inductive proximity switches comprising a reference current source IREF connected between a reference voltage supply rail and a first side of a current mirror, a second side of the current mirror being connected to a proximity switch rectifier, the first side of the current mirror being connected to a capacitor CINT and to one input of a two input comparator, the other input of the comparator being held at a threshold level, wherein a fixed hysteresis current source IHYST is provided in parallel with the current reference source IREF, the fixed hysteresis current source IHYST producing a switchable current which is a fixed proportion of the current of the current reference source IREF, the fixed hysteresis current source IHYST being switched on (off) when a target is detected and off (on) when no target is detected. This invention provides for reduction of effects detrimental to the speed of operation of the switch.