GB806559A - Transistor switching device - Google Patents

Abstract

806,559. Transistor relay circuits. SOURGENS, R., and CHOLLET, R. Feb. 21, 1957 [Feb. 29, 1956], No. 5846/57. Class 40 (6). In a circuit in which the supply potential B, Fig. 1, exceeds the safe potential to be applied across the emitter-collector path of transistors 1, 2 the emitter of each is directly connected to the collector of the preceding transistor with the final transistor connected to a load 27 and the input applied to the base-emitter path of the first transistor. The collector of each transistor is connected to the supply over resistors 22, 23 with a resistor 21 connected between the junction of the resistors 22, 23 and earth. The value of the resistors 21, 23 is so chosen that when the transistors 1, 2 are cut-off the potential existing across the emitter-collector path does not exceed the safe value. Assuming transistor 1 to be cut-off the collector potential is negative with respect to earth causing the emitter to cutoff the next transistor 2 so that the load 27 is not energized. When a negative-going potential is applied to the base of transistor 1 the transistor passes collector current, causing the collector potential to rise and therefore the emitter potential of transistor 2 so that it also passes current to energize the output load 27 which may be a relay. In order to obtain a more effective cut-off a resistor 24 of low value may be included between the resistors 22, 23 and the base of the transistor 2. In a modification, Fig. 2 (not shown), four transistors are arranged in cascade with the resistors 21, 23 graded according to a given formula to provide the correct operating potentials between emitter and base in the cut-off condition.