| 摘要 |
A power transistor in the final stage of an IC amplifier feeding a reactive load, such as a loudspeaker, has an emitter resistor connected across the input of a heat-sensitive monitoring transistor by way of a diode in bucking relationship with its base/emitter path, the monitoring transistor being part of a protective circuit which reduces the input signal to the power amplifier in the event of an overload. The monitoring transistor is separated from the power transistor, on the silicon chip of the amplifier, by a distance so chosen that an overload raising the temperature of the power amplifier will significantly reduce the operating threshold of the monitoring transistor only if the overload persists for a minimum period on the order of one millisecond. To minimize the dependency of the sensitivity of the protective circuit upon ambient temperature, the diode is also of heat-sensitive character and is positioned on the chip at a distance from the power transistor greater than that of the monitoring transistor so as to compensate in part for the lowering of its threshold in the case of longer-lasting temperature rises. |
