Patent ID: 7256976

Claim:
An electrostatic discharge protective circuit comprising: a first node; a second node which is electrically isolated from the first node during a normal operation state when there is no ESD voltage across the first and the second nodes; an ESD protective circuit which has a trigger terminal and forms a discharge path from the first node to the second node when trigger signals are applied to the trigger terminal; and a trigger circuit including a first MOS device and a second MOS device, the first MOS device being connected in a circuit to be protected as a constituent thereof and also being connected between the first and second nodes, the first MOS device having a source and a drain one of which is connected to the first node, functioning as a part of the circuit to be protected during the normal operation state when an ESD voltage is not applied, and forming a conductive path between the drain and the source thereof when an ESD voltage of a predetermined value or more is applied to the first node during the normal operation state, the second MOS device having a source and a drain connected between the other of the source and the drain of the first MOS device and the trigger terminal of the ESD protective circuit and a gate connected to receive a power source voltage for setting the second MOS device in a non-conductive state during the normal operation state, for supplying the trigger signals to the trigger terminal of the ESD protective circuit when the first MOS device becomes conductive.