Patent ID: 7746611

Claim:
An ESD protective circuit comprising: a contact terminal; a first supply voltage terminal for a first supply potential; a second supply voltage terminal for a second supply potential, wherein the first supply potential is higher than the second supply potential; a n-p-n bipolar transistor chain comprising a plurality of n-p-n bipolar transistors, wherein collector terminals of the n-p-n bipolar transistors are connected to the first supply voltage terminal, wherein a base terminal of a first n-p-n bipolar transistor of the n-p-n bipolar transistor chain is connected to the second supply voltage terminal, wherein base terminals of the remaining n-p-n bipolar transistors are connected each to an emitter terminal of a previous n-p-n bipolar transistor, and wherein the emitter terminal of a last n-p-n bipolar transistor of the n-p-n bipolar transistor chain is connected to the contact terminal; and a current source which is connected to an emitter terminal of at least one of the n-p-n bipolar transistors of the n-p-n bipolar transistor chain, wherein the current source includes a voltage reducing circuit which is connected between the first and second supply voltage terminals and is able to generate a voltage lower compared to the second supply potential, and wherein the current source is able to provide a current which compensates, up to a maximum tolerable voltage deviation from the second supply potential at the contact terminal, a current flowing from the emitter terminal.