| 摘要 |
PURPOSE:To protect an inner circuit from malfunction by a method wherein a switching element is provided between a power source wire and an electrostatically protective element. CONSTITUTION:When a high voltage is applied between an external connection terminal 3 and a power source wire 1, the high voltage is applied to the base of a switching element 7-1 through the intermediary of a switching element 7-2 which is in an ON- state to turn the switching element 7-1 ON. Then, a voltage is applied to an electrostatically protective element 4 almost concurrently when the switching element 7-1 is turned ON. At this point, as a voltage is applied to the forward side of the diode of the element 4, a current path is established between the external terminal 3 and the power source wire 1. By this setup, the voltage between the external terminal 3 and the power source wire 1 is clamped down to a voltage of 0.7-1V or the forward voltage of the diode. On the other hand, when a voltage is applied to the external connection terminal 3 at the time when a power source voltage is not applied, as the switching element 7-2 is in an OFF-state, the switching element 7-1 is also in an OFF-state, so that a current path is not established between the external power wire 1 and the external connection terminal 3 and concurrently an LSI to which a power is not supplied hardly malfunctions. |
