Distortion free power limiting and clipping prevention circuit

摘要

A circuit for limiting the output power of a power amplifier to a preselected value in order to prevent the amplifier from either clipping the input signal or applying potentially damaging signal levels to a loudspeaker connected to the output of the amplifier. The limiting and clipping circuit includes a voltage controlled attenuator through which the input signal passes before entering the amplifier. The amplifier output is compared to an output reference by a control circuit which supplies an attenuation command to the attenuator whenever the output level reaches the reference level. The value of the output reference can be easily adjusted from a fairly low percentage of the amplifier power capacity to the amplifier's maximum power capacity in which condition the circuit prevents amplifier clipping. The circuit is relatively quick to attenuate input signals responsive to excessive output levels, but is relatively slow to reduce the attenuation when the output level is subsequently lowered. Consequently, the circuitry quickly limits the output to safe and distortion free limits without itself introducing waveform distortion of signals in the audio range. Various embodiments of the invention may be employed depending upon specific circumstances.