Transistor power amplifier circuit

摘要

Two output transistors constituting a push-pull output amplifier circuit are connected in series between a power supply and a grounded point, and an output terminal is disposed at a point where the two output transistors are commonly connected. An operation detector circuit detects the operation of one output transistor. A level detector circuit detects a d-c voltage level at the output terminal. The two output transistors are driven by a drive circuit in a push-pull manner. The output of the operation detector circuit and the output of the level detector circuit control the drive circuit via a control circuit. When the operation detector circuit detected the fact that the operation of one output transistor has deviated beyond a predetermined detection level, the control circuit works to confine the operation of the abovementioned output transistor within a predetermined restriction level via the drive circuit. The power loss in the restriction level is smaller than the power loss in the detection level. During a period in which the output terminal is short-circuited to the grounded point in a d-c manner, the level detector circuit so controls the control circuit that the operation of the abovementioned one output transistor is confined within the restriction level.