Overvoltage protection circuit with overvoltage removal sensing

摘要

An overvoltage protection circuit arranged to sense removal of the overvoltage condition. The protection circuit blocks current passing through a pull up transistor of an output circuit to a high-potential supply rail during an overvoltage condition applied at a common bus. The protection circuit includes one protection branch controlled by the potential at the bus and powered by the high-potential supply rail of the output circuit to be protected. The protection circuit also includes a second protection branch controlled by the high-potential supply rail and powered by the potential on the bus. When an overvoltage condition occurs, the second branch is activated and regulates an output from the first protection branch. That output signal controls the control node of the pull up transistor of the output circuit to be protected. The two protection branches are configured such that removal of the overvoltage condition causes a rapid changing of the state of the output of the first protection branch so that the operating condition of the pull up transistor remains the same as it was prior to the overvoltage condition.