Abstract: A gain control circuit (10) of an amplifier (3) for listening via a loudspeaker (4) in an apparatus, more specifically a telephone set, which includes a microphone (1), in order to suppress the Larsen effect. The gain control circuit comprises first control means (100) which control a first gain reduction of the amplifier (3) when the amplitude of the microphone signal (S) exceeds a first predetermined threshold determined by a first reference voltage VR1, in dependence on a first time constant (RD1+RD2.C). The gain control circuit also includes second control means (200) which start operating only after the said first time constant, and provide a supplementary reduction of the gain depending on a second time constant (RD2.C) which is shorter than the first time constant, as long as the amplitude of the microphone signal (S) exceeds a second threshold, which is lower than the first threshold, determined by a second reference voltage VR2.

Abstract: A motor-car headlight with a built-in static relay.The headlight lamp is connected in series with a power phototransistor with which it is optically coupled. Turn on and turn off of the phototransistor is effected by temporarily changing the base voltage.

Abstract: A power limiting device for an electric heating system electronically controlled by a modulating thermostat includes a bistable trigger circuit having an auxiliary temperature sensor preferably comprising a temperature dependent resistor. The trigger circuit controls the modulating thermostat to change the on/off ratio of the heating system as a function of a second temperature parameter to which the auxiliary temperature sensor responds.