Abstract: An apparatus for improving the salient properties of the output stages of electronic power amplifiers v.s. varying load conditions. A novel circuit, based on current feedback sensing the instantaneous drive current of the output devices, is used to linearize the output characteristics of the output devices. The important features, compared with the presently known and employed drive circuits, relate to a more linear transfer characteristic, much larger output current capability, and more output amplifier design.

Abstract: Apparatus for electronically protecting output transistors of electronic amplifiers against thermal overload, overcurrent, overvoltage, and second breakdown mechanism. An analog multiplier circuit, together with a novel circuitry for deriving the instantaneous voltages across, and the currents through, each of the output transistors, is used to obtain the instantaneous power dissipation in the transistors. A thermal sensor, the electrical signal of which is used as an additional variable in the multiplication, yields the thermal derating necessary for the transistors, and an integrating time constant used to weigh the output signal of the multiplier, takes into account the time derating of the transistors.