Patent ID: 6737905
Filing Date: 2004-05-18
Classification: G05F,H03K

Abstract:
A clamp circuit which is incorporated in an IC and clamps an input voltage inputted into an input terminal of said IC, comprising:an input voltage detecting circuit for outputting a detected voltage, wherein a first resistance circuit and a first transistor in a form of a source follower or emitter follower are connected in series between first and second supply lines and said input voltage is inputted into a control terminal of said first transistor and said detected voltage is outputted from said first resistance circuit; a reference voltage generating circuit for outputting a reference voltage, wherein a second resistance circuit and a second transistor in a form of a source follower or emitter follower are connected in series between said first and second supply lines and a voltage of said second supply line is inputted into a control terminal of said second transistor and said reference voltage is outputted from said second resistance circuit; a comparator for outputting an instruction signal instructing to clamp said input voltage, when said detected voltage goes across said reference voltage on the basis of comparison of said detected voltage with said reference voltage; and a switching circuit connected between said input terminal and said first or second supply line, said switching circuit being switched on, under such a condition that said instruction signal is outputted from said comparator.