GB982129A - Improvements in or relating to transistor circuits - Google Patents

Abstract

982,129. Transistor amplifying circuits. STANDARD TELEPHONES & CABLES Ltd. Dec. 31, 1963, No. 51337/63. Heading H3T. The invention relates to a transistor amplifier circuit utilizing transistors T1, T2 in cascade connection, i.e. with their emittercollector paths connected in series, so as to obtain a larger voltage output swing than can be obtained from a single transistor. The base of transistor T1 is biased by means of an emitter circuit resistor R3 and the base of transistor T2 by means of a potentiometer R4, R5 across the supply. In such a circuit there is the danger of the transistors being driven beyond their allowable emitter to collector voltage rating on peak input swings; this is prevented, according to the invention by connecting a diode D1 across the base to emitter path of the transistor T2. The diode is poled to conduct in the opposite direction to that path and is rendered conductive by means of a resistor R1 of high value connected to the supply line. The arrangement may be extended to use three or more transistors in series, the base of each of the transistors with the exception of the first being biased via a separate potentiometer. Capacitors may be connected between each base and earth in order to prevent overshoot on the occurrence of sharp large transcents in the input signal voltage.