| 摘要 |
A protection circuit (10) for a power amplifier mutes the amplifier if the average power dissipated in the amplifier output stage exceeds a predetermined limit. A ground referenced current detector (28) monitors the current through the amplifier output stage, producing a current signal (30) that is directly proportional to this output current. Similarly, an absolute voltage detector (32) monitors the voltage across the output stage, producing a voltage signal (34) that is directly proportional thereto. The current signal and voltage signal are input to a multiplier (36), which multiplies them to determine their product, producing a power signal (38), which is directly proportional to the power dissipated in the output stage. This power signal is filtered to represent the average power dissipation in the ouput stage. The filtered signal (42) is then compared (44) to a threshold signal representing a predefined power dissipation limit. A monostable multi-vibrator (46) periodically mutes the amplifier so long as the power dissipated exceeds the predefined limit. In addition to being used for muting the power amplifier, the filtered power output signal (42) is employed for controlling the speed of a cooling fan.
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