A so-called switching voltage regulator for an interface circuit in a telephone subscriber line, being of a type adapted to control the on/off states of an electronic switch, connected to the interface circuit and consisting of first and second transistors interconnected into a Darlington arrangement, comprises an ON-state sensor connected as an input to the collector of the first transistor and an OFF-state sensor connected as an input to the base of the first transistor, and a pair of current extractor devices respectively associated with the related bases of the first and second transistors. Also provided are first and second current sources, each connected to a corresponding current amplifier. The first of the amplifiers powers both current extractor devices. The second amplifier and a third current source are connected to the base of the second transistor. A first gate has an input associated with the output of the OFF-state sensor via a storage cell, and a second gate has an input associated with the output of the ON-state sensor via a further storage cell. Each amplifier is respectively connected the outputs of the first and second logic gates, each gate receiving on the other input an appropriate enable signal from the regulator. The hold current source connected to receive the enable signal of the second logic gate. Such a regulator can minimize the current draw from the high voltage power supply (-50 Volts) and make the electronic switch connected to the telephone subscriber line switch faster.