| 摘要 |
PURPOSE:To eliminate high dielectric strength/high power parts and to reduce the cost of a circuit by providing a switch means which is connected to both ends of a constant voltage element and which comes to a short-circuited state when a current exceeding a prescribed value flows in a transistor. CONSTITUTION:When a line A is grounded an an overcurrent is generated, the overcurrent flows in a resistance R2 through Tr2. When the voltage VR2 of the resistance R2 exceeds a voltage VBE (about 0.7V) between the base.emitter of Tr3, Tr3 is turned on, Tr4 connected to the collector of Tr3 is also turned on and a system comes to an operation state. When Tr4 is turned on, the voltage of both ends of Zener diode DZ 1 comes to a voltage VCETr4(sat) (about 0.2V) between the collector and the emitter in a saturated state in Tr4 and it comes to almost the short-circuited state. |
