Patent ID: 6359490
Filing Date: 2002-03-19
Classification: H03K

Abstract:
A clamping circuit comprising:a first circuit containing a first transistor and a first diode electrically connected in series between the input terminal and the first voltage feed line, and a first voltage feed terminal for feeding the first voltage to the control terminal of said first transistor; a second circuit containing a second transistor and a second diode electrically connected in series between said input terminal and the second voltage feed line, and a second voltage feed terminal for feeding the second voltage to the control terminal of said second transistor; whereby when the voltage between said first voltage feed terminal and said input terminal or the voltage between said second voltage feed terminal and said input terminal reaches a prescribed level, said first or second transistor becomes conductive and the voltage of said input terminal is clamped; first, second and third resistive elements connected in series between said first voltage feed line and said second voltage feed line; the connection point between said first resistive element and said second resistive element forming said first voltage feed terminal; and the connection point between said second resistive element and said third resistive element forming said second voltage feed terminal; wherein the cathode of said first diode is connected to said input terminal; said first transistor is connected between the anode of said further diode and said first voltage feed line; the anode of said second diode is connected to said input terminal; said second transistor is connected between the cathode of said second diode and said second voltage feed line; the power source voltage is fed to said first voltage feed line; and the ground voltage is fed to said second voltage feed line; and wherein a third transistor connected between said first voltage feed terminal and said second voltage feed terminal; whereby controlling the voltage applied to the control terminal of said third transistor, the voltages at said first and second voltage feed terminals are changed.