Abstract: A description is given of a communication set for connection to a communication line such as a telephone line, which communication set includes means for detecting set functions such as ringing signal detection, and a rectifier circuit which is connected to a common output which is coupled to a scanning device included in the set function detection means, which scanning device detects the line conditions. A large number of line conditions may be detected with a minimum of components required, among which an analog/digital converter for which only a single input pin on a chip is necessary.

Abstract: The invention relates to a control circuit for amplified listening having a shunt regulator (A.sub.0, T.sub.1) controlling at a value V.sub.0 the supply voltage V.sub.B of an amplifier feeding a loudspeaker (1) for amplified listening, having a gain control input (G). When the regulator conducts an excessive current I.sub.s, a switch (20) is closed and a storage capacitor (C.sub.1g) is charged by a current source (SC). A threshold amplifier (A.sub.2) opens a transistor (T.sub.4) when the voltage V.sub.B falls below V.sub.1 (V.sub.1 <V.sub.0). The capacitor (C.sub.1g) is then rapidly discharged through resistor R.sub.1g (and R.sub.2g).

Abstract: A telephone set comprising an active line voltage stabilizer circuit having two output terminals 10-1 and 10-2 between which it produces a stabilized direct voltage which is independent of the line current. A series arrangement of a capacitor (14) and a resistor (16) is connected between such output terminals, the junction thereof constituting a DC supply terminal for the telephone set. Such arrangement does not alter the a.c. impedance of the stabilizer circuit between the wires, and has a considerably lower d.c. output resistance than supply terminals previously employed.

Abstract: A transmit amplifier which also stabilizes the line direct voltage of the audio transmission circuit of a telephone set with respect to a reference voltage, the amplifier gain being adjustable to a high value by means of a resistor which does not affect the further properties of the audio transmission circuit. Variation of the line direct voltage by the offset current of the microphone pre-amplifier preceding the transmit amplifier, and by temperature fluctuations of the reference voltage, is greatly reduced by increasing the reference voltage and adding a temperature-dependent current source to a voltage divider which is comprised in the amplifier.

Abstract: The telephone amplifier of an audio transmission circuit comprises a class-B output stage as a result of which the required supply current of this amplifier is considerably lower than with prior art telephone amplifiers. A distorting voltage produced by the current signal in the supply current of the glass-B output stage does not affect the output signal of the telephone amplifier because the input stage and the output stage each comprise their own setting circuits which produce mutually independent setting voltages.

Abstract: Two current circuits are between two common terminals (+V.sub.B and -V.sub.B). The ratio between the currents in the two current circuits is defined by a first current-dividing circuit, and the absolute values of these currents are defined by means of a second current-dividing circuit, in particular a resistor in this second current-dividing circuit. In order to ensure that the current-stabilizing assumes the proper state upon activation, a first current-supply circuit is coupled to the input of the second current-dividing circuit, which current-supply circuit comprises the series arrangement of a resistor and a transistor arranged as a diode, and a second current-supply circuit is coupled to the output of the current-dividing circuit, which second current-supply circuit includes a transistor whose base is connected in common with that of the transistor of the first current-supply circuit.