Abstract: Transistor switching means in which a principal transistor (T.sub.5) feeds into a load (R.sub.c) when a control signal saturates a control transistor (T.sub.1), a resistance bridge (R.sub.3,R.sub.4) fed by a source (V.sub.AL) then polarizing the base of the principal transistor (T.sub.5).An auxiliary transistor (T.sub.3 a) has its base coupled to the collector of the transistor (T.sub.5) by means of a diode (D.sub.2 a) and one of the two polarization resistances (R.sub.10 -R.sub.11). When the collector-emitter voltage of the principal transistor becomes too strong as a result of a short-circuit in the load, the auxiliary transistor (T.sub.3 a) is saturated and blocks the principal transistor (T.sub.5).Application to detectors of the type having an electro-luminescent diode excited by pulses; these pulses, applied to the auxiliary transistor (T.sub.3 a) block it momentarily in order to ensure the re-setting of the circuit when the overload has disappeared.

Abstract: Photo-electric detector comprising a multivibrator with two complementary transistors (T.sub.3 and T.sub.4) of which the base of the first is coupled to the collector of the second by a time constant circuit (R.sub.5 -R.sub.6 -C.sub.1) comprising a resistance (R.sub.5) with negative temperature coefficient. This multivibrator excites an electro-luminescent diode (D.sub.1) which cooperates with a photo-transistor (T.sub.1). After integration, the received signals control a commutator (thyristors Th.sub.1 and Th.sub.2). The circuit is fed by a rectifier bridge with diodes (D.sub.11 to D.sub.14) and formed with two wires.Application to the detection of the presence of an object which blocks the luminous beam emitted by the diode (D.sub.1).

Abstract: A direct current proximity detector having a first terminal directly connected, to a terminal of a supply source and second and third terminals connected to the other terminal of the supply source through a load, an oscillator associated with a detector of its state of oscillation, a voltage stabilizer and a static switching device. The switching device comprises first and second transistors, the conducting state of the respective transistors depending upon the state of a corresponding output of an inverter unit which is controlled by the detector. The two transistors are connected to the first terminal through a Zener diode, second and third terminals being interconnected by means of two serially connected diodes of opposed polarities the common point of which supplies the voltage stabilizer.