| 摘要 |
PURPOSE:To enable protection against excess current without using a conventional current detecting element by connecting an integration circuit to a driving signal source in parallel, connecting a discharge circuit to a capacitor of this circuit and short-circuiting the controlling electrode of a driven element through other switching element when terminal voltage exceeds a specified value. CONSTITUTION:A normally off voltage driving type semiconductor element 11 is made a driven element. An integration circuit consisting of a resistance 13 and a capacitor 14 is connected in parallel to a driving signal source 12, and a diode 15 is connected to the capacitor 14. A resistance 18 for preventing short-circuiting of the output of the driving signal source 12 when a semiconductor switch 16 is made on is provided. Thus, the on voltage of the driven element 11 can be known exactly by terminal voltage of the capacitor 14, and when the terminal voltage exceeds voltage of a constant voltage diode 17, the semiconductor switch 16 is turned on and turns off the driven element 11. |
