Abstract: A composite video signal each line of which comprises a line synchronizing pulse, a front and a back porch and a vision portion, the synchronizing pulse of which may contain a burst of pulsed additional information is applied to an input terminal (1) which is connected to the input of a first signal path (T1, T2) whose output is connected to a current source (I1) and to an output terminal (8). A second signal path (T3, T4) has its input connected to a reference voltage input (5) and its output connected to the current source (I1) and the output terminal (8). A switching circuit (T5, T6) alternately enables the first and second signal paths (T1, T2; T3, T4) under the control of a switching signal at a connection (10) such that the output terminal (8) produces a composite video signal in which the synchronizing pulse at the input terminal is replaced by a pulse or level. The replacement does not contain the burst of pulsed additional information when present in the applied signal.

Abstract: A high voltage power transistor circuit composed of a pair of transistors (TR1, TR2) serially connected through an inductor (L) to a supply voltage. Associated components are connected to the transistors which determine various periods of operation. In order to ensure that the transistors (TR1, TR2) are rendered non-conducting simultaneously, sensors (S1, S2) sense their change in base current to produce pulses in monostable multivibrators (M1, M2) whose relative phases are compared in a digital phase comparator (PC). The drive for each transistor (TR1, TR2) is provided by an associated driver stage (DR1, DR2) via an associated device (DC1, DC2) having a characteristic used to control the cut-off of its associated transistor. One of the devices (DC2) has a variable characteristic which is controlled by the output of the phase comparator (PC) to ensure the required simultaneous non-conduction of the transistors.