Patent GB-809401-A (GB)
Title: Improvements in or relating to circuit arrangements employing transistors
Inventor: JANSSON LEONARD ERIC
IPC: H02M7/5375
Filed: 1957-08-02
Abstract: 809,401. Transistor amplifying circuits. MULLARD Ltd. Aug. 2, 1957, No. 24589/57. Class 40 (6). In a circuit employing a number of seriesconnected transistors including a first transistor and a number of auxiliary transistors with a load in series with the combination, a potentiometer arrangement is connected effectively in parallel with the transistors with the base of each auxiliary transistor connected to the potentiometer to maintain a desired potential drop across each transistor. The circuit enables a number of transistors to be employed where the supply potential exceeds the safe collector potential of a single transistor and the circuit described employs junction transistors, although point contact and field effect transistors may be used. In a common base amplifier, Fig. 1, the input is applied to the emitter of a first transistor TR1 connected to the emitter of an auxiliary transistor TR2 with a load R1 in its collector circuit. Assuming the resistors R2, R3 to be of equal value, the base potential of transistor TR2 is set at half the potential existing between the input and output and due to emitter follower action the emitter of TR2 and hence the collector of transistor TR1 are near this potential so that substantially equal emittercollector potentials occur across each transistor. The transistor TR1 may be connected in the common emitter manner, Fig. 2 (not shown), and a number of auxiliary transistors may be employed, Fig. 3 (not shown). With this arrangement the resistor R2 has to carry all the base currents of the auxiliary transistors so that distribution of potential is not complete. In a modification, Fig. 4, this defect is overcome by arranging two potential dividers R2, R4 and R3, R5 and R6. Each element such as R4 bridges two transistors TR2, TR3 with a tapping to the base of one transistor TR3 to set the emitter potential which forms one end of the next divider R5, R6, which in turn sets the base potential and hence the emitter of transistor TR2. A pair of circuits may be combined with a common emitter resistor to provide a push-pull output from a single input, Fig. 5 (not shown). The load resistor R1 may be transferred to the other terminal of the supply, Fig. 6 (not shown). In order to permit a larger base current in transistor TR2 the value of the resistors R2, R3 is reduced, Fig. 7, and they form the emitter load of further transistors TR3, TR4. This process may be continued by inserting a further emitter follower transistor TR5 in the base lead of transistor TR2. In a further circuit, Fig. 8, the transistors TR1, TR2 are duplicated by transistors TR1a, TR2a of opposite conductivity type. With the point C connected to the centre tap of the battery a balanced input is applied at points A and B. Alternatively either A or B may be joined to the centre tap of a battery and the input applied to the other terminal B or A. The connection to the centre of a battery may be avoided by employing a potential divider across the points D and E with one of the terminals A, B connected to the centre, in which case either of the loads R1 or R1a may be dispensed with and the output taken from the other load.