an output stage and feedback circuit for a buffer amplifier are disclosed . the output stage protects an operational - amplifier circuit preceding it from overvoltages appearing at the load . the circuit includes a pair of complementary transistors in a push - pull arrangement that sources and sinks current to and from the load . both the transistors are in common - emitter configurations , and each one has a corresponding diode connected between its collector and the load in an orientation opposite that of the collector - base junction . the diodes prevent the reverse current that would otherwise flow in response to an output overvoltage of the polarity that forward biases the collector - base junction of the transistor , and the over - voltage is thereby prevented from being seen at the operational - amplifier output terminal . overvoltages of the other polarity are not seen because they reverse bias the base - collector junction . each amplifier transistor also has associated with it an auxiliary transistor whose base is connected through a zener diode to the output terminal of the circuit . the auxiliary transistor is connected between the output - stage amplifier and a source voltage . an output overvoltage of the right polarity and sufficiently large to turn on the zener diode therefore turns on the auxiliary transistor . this turns off the amplifier transistor that would otherwise be on , thereby preventing thermal destruction of the amplifier transistor .