Protection circuit for power amplifier

摘要

A directional coupler is provided on the output side of a power amplifier. An increase in reflected wave power from a load is detected through the directional coupler by an electric power detector (wave detector). Then, a detection signal of an electric power detector is provided to a power amplifier supply voltage control circuit. As a result, the supply voltage supplied to the power amplifier is reduced gradually. By virtue of this, the supply voltage provided to the power amplifier is gradually reduced when the power amplifier approaches a breakdown condition. This protects the power amplifier.