| 摘要 |
PURPOSE:To improve the protection effect by detecting a voltage of collector- emitter of a power transistor (TR) by a voltage detector so as to detect an overcurrent thereby reducing the interruption time of the overcurrent. CONSTITUTION:In addition to a similar protection circuit as a conventional circuit, a collector-emitter voltage VCE of the power TR 1 is detected by a voltage detector 8, the detected voltage activates a base drive circuit 2 to interrupt the current of the TR 1. The voltage VCE shown a characteristic shown in figure with respect to a collector current IC when the base current is constant. In setting the detection point of the voltage detector 8 to a value within both voltages V1 and V2 where the voltage VCE changes linearly, e.g., a current I1, when the collector current IC of the TR 1 increases from the current I1 and the voltage VCE is increased, the voltage detector 8 detects it and the collector current IC is interrupted via the base drive circuit 2. Thus, not only the interruption time is reduced but also the protection circuit is duplicated. |
