GB914294A - Improvements in or relating to electronic switching devices - Google Patents

Abstract

914,294. Transistor switching - circuits. ROCHAR ELECTRONIQUE. April 7, 1961 [April 9, 1960], No. 12611/61. Class 40 (6). [Also in Group XXXVIII] A transistor switching circuit comprises two transistors 3, 4, of opposite conductivity types, having their collectors connected together to an output terminal 6, and their emitters connected across a source of reference potential 7; and a third transistor 8, of the same conductivity as transistor 3, having its base connected to the emitter of transistor 3, its emitter connected to the base of transistor 3, and its collector connected to the base of transistor 4; the arrangement being such that when no input signal is applied to the base of transistor 3, it is conductive and transistors 4, 8 are cut-off, and when an input signal is present, transistor 3 is cut-off, and transistors 4, 8 are conductive. With no input signal present bias source 9 biases PNP transistor 3 on, and PNP transistor 8 off and bias source 12 biases NPN transistor 4 off. Application of a signal of the appropriate polarity to the input 1, 2 produces a potential which opposes bias 9 cutting transistor 3 off and switching transistor 8 on, and the change in potential across resistor 14 due to the collector current of transistor 8 is sufficient to switch transistor 4 on. Diode 11 is provided to limit the baseemitter potential across transistor 4. The circuit may form part of a digital-to-analogue converter, one circuit as described being associated with each sealer. Output resistors 6 are then made proportional to the weighted coefficient of each sealer. If the polarities of the biases and the conductivity type of transistor 8 are reversed the functions of transistors 3, 4 may also be reversed.