| 摘要 |
A device is disclosed for protecting against shorts the transistors of the push-pull stage in a power amplifier operating on a low voltage supply, in particular for car radio sets. The device comprises sensors which are responsive to currents flowing through the two transistors which form the amplifier push-pull stage, and current-to-voltage converters which convert the sensed currents into corresponding respective voltage signals. The latter are compared in respective voltage-comparing circuits with a reference voltage indicative of the highest admissible current through either of the transistors while the other is shorted. The device also comprises two additional voltage comparators wherein the voltage applied to the load, which may be of a resistive or a reactive type, is compared with a set reference voltage which is lower than or in the extreme equal to, in absolute value, the voltage supply to the amplifier push-pull stage. If the voltages being compared exceed in absolute value the set reference voltages, then the output signals from the comparators energize either of the two bistable circuits to cut off the power supply to the amplifier. The device affords a clear cut between shorted and normal operation conditions, and requires no high current peaks to become operative and activate the protection. After the shorted condition is removed, the device provides automatically for restoring the power supply to the amplifier.
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