| 摘要 |
PURPOSE:To prevent a transistor from being broken down by a short circuit current by supplying and cutting off a base current by one DC power source, also detecting the short circuit current, and suppressing the base current, in a base driving circuit of a transistor. CONSTITUTION:When a driving signal is inputted to a terminal 4, a transistor 6 becomes on, and it is turned on by supplying a base current of a transistor 9. On the contrary, when a cut-off signal is inputted, the transistor 6 becomes off, a transistor 8 becomes on because the base current is supplied through a diode 13 and a Zener diode 15, the base potential of the transistor 9 is lowered to about the emitter potential, and the transistor 9 is turned off at a high speed. Also, in case when a short circuit current flow to the transistor 9, this collector- emitter voltage rises, but the current flows to the Zener diode through a voltage dividing circuit consisting of resistances 17, 19, the transistor 8 is turned on, the base current of the transistor 9 is suppressed, and a breakdown by the short circuit durrent is prevented. |
