Single ended single supply class AB output stage

This circuit was an experimental DIY project designed / built to replace a single xstr class A audio driver. The result was a much cooler running output stage. The input amp is a CE stage with some of the emitter degeneration bypassed to help increase the forward loop gain. The collector load is a Vbe multiplier used to help eliminate crossover distortion and reduce the quiescent current of the output npn / pnp xstrs. Included in the collector load is the output xstr. The loop is closed thru the 10k and 4.7k resistors whose primary function is to set the dc op and closed loop gain. The circuit from the base of the input xstr to the load is a transimpedance amplifier with a hand calculated close loop gain of approx 6.93k V/A. Using the 3.3k source resistance, the calculated approx voltage gain from the input source to the load is then 6.4 db (2.1). A comparison of the hand calc approx, simulation, and hardware meas of the closed loop voltage gain is as follows. Calc : 6.4 db (2.1) vs Sim : 5.11db (1.8) vs Meas : 5.1 db (1.8). To observe the DC op, disconnect the lead from the AC source to the 3.3k resistor and run the transient analyisis test.

published 8 years ago