GB901457A - Improvements in or relating to transistor d.c. amplifiers - Google Patents

Abstract

901,457. Transistor amplifier circuits. FERGUSON RADIO CORPORATION Ltd. Jan. 27, 1959 [Jan. 27, 1958], No. 2709/58. Class 40 (6). A push-pull transistor D.C. amplifier comprises a first adjustable potentiometer connected between two like electrodes of respective transistors to apply relatively adjustable proportions of a temperature independent voltage thereto and a second adjustable potentiometer connected to apply relatively adjustable proportions of a temperature-dependent potential to the electrodes, means being provided for varying one of the potentials. The amplifier shown in Fig. 1 has input terminals TI 1 and TI 2 , and output terminals TP 1 and TO 2 . The emitters are connected together so that with no input circuit connected to the terminals the bases are at substantially the same potential. Resistor VR3 may therefore be adjusted at a first temperature such that the base potentials are made equal to the potential applied to the tap on potentiometer VR1 and the transistor currents are accordingly independent of the setting of this potentiometer. Potentiometer VR2 is now adjusted to balance the collector currents or to provide a required amount of unbalance. The common emitter potential of the transistors is applied to a difference type amplifier A so that small changes of emitter current with changes in temperature provide relatively large changes at the output of the amplifier A. Accordingly at a second temperature a different potential is applied to the tap on VR1 and this potentiometer may be adjusted to provide a desired degree of balance without changing the balance conditions at the first temperature. When the input terminals are connected to a low impedance source the two balancing potentiometers may be connected to the emitters (Fig. 2, not shown) and when the input circuit may be of either high or low impedance, potentiometers may be connected in both base and emitter circuits (Fig. 3, not shown). Either or both the temperaturedependent potentials may alternatively be derived externally of the amplifier.