GB926762A - An arrangement for controlling switching transistors - Google Patents

Abstract

926,762. Transistor switching circuits. LICENTIA PATENT-VERWALTUNGS-G.m.b.H. Jan. 1, 1960 [Jan. 9, 1959], No. 65/60. Class 40 (6). In an arrangement for controlling a number of switching transistors 2, 3, Fig. 1, a first current path comprising a transistor 1 in series with a resistor 8 and a second path comprising a unidirectionally conducting device, such as a semi-conductor diode 12 in series with a resistor 9 are connected in parallel between supply terminals 4, 5, the arrangement being such that the diode 12 has a threshold voltage greater than the voltage drop of the collector-emitter path of the transistor when conducting. When switch 15 is open cutting off transistor 1, current flows through diode 12 and resistor 9, making terminal 10 negative with respect to terminal 11 so that transistor 2 is conductive, connecting load 47 to supply 51, and transistor 3 is cut off. Closing switch 15 switches transistor 1 on, and current flows through resistor 8, making terminal 10 positive with respect to terminal 11, switching on transistor 3, and cutting transistor 2 off. In a modified arrangement, Fig. 2, two control transistors 18, 19 are used to control three switching transistors 27, 28, 29 to connect load 43, 44 or 45 to its respective supply 53, 54, 55 according to whether transistor 18, transistor 19 or neither is conducting. Fig. 3 (not shown) is a modified arrangement of the circuit of Fig. 2 to allow the emitters of the switching transistors 27, 28, 29 to be connected to a common point. Other non-linear devices, such as a Zener diode, a biased diode or a selenium rectifier comprising a plurality of elements may be used as the device 12.