True-class B amplifier

EE July/August 1986 30 true class B amplifier The quiescent current in this ampli- fier is always nought, so there is no need for zero setting or for a circuit to prevent thermal run-away. Com- plexity is further reduced by the use of a single supply voltage, Voltage divider Ri-R2-R3 fixes the voltage level at the base of Ti at just above half that of the supply voltage. Since a current source, consisting of T3, R7, Di, and Dz, has been included in the collector circuit of Tz, this stage provides a very high voltage amplification. The return line of the current source is connected to the output, so that the voltage necessary to stabilize the source does not limit the dynamic push-pull characteristic. The current source has, therefore, a high-impedance character. The complementary power ampli- fiers, T4 and Ts, are darlington tran- sistors, which, of course, enable the collector current in the driver stage to be kept relatively low. The feedback to the emitter of Ti via R5 and Re d...