Patent ID: 7869176

Claim:
An overvoltage protection circuit for protecting a pass element in a controlled voltage supply circuit electrically connected between a circuit power supply interconnection terminal region suited for electrical connection to a circuit power supply and an output terminal region between which the pass element can be directed at a control region thereof to provide a conductive path of a selected conductivity, the pass element being protected from voltage surges that may occur on the circuit power supply interconnection with respect to a voltage reference interconnection, the circuit comprising: a first voltage reference capable of maintaining a substantially constant selected voltage between a pair of terminating regions for a range of electrical currents through that pair of terminating regions, a second voltage reference capable of maintaining a substantially constant selected voltage between a pair of terminating regions for a range of electrical currents through that pair of terminating regions, one of the pair of terminating regions of the second voltage reference being electrically connected to the pass element at only the control input thereof and the other being electrically connected to the voltage reference interconnection, a voltage divider capable of maintaining at an output thereof a selected fraction of the voltage between a pair of terminating regions, the voltage divider and the first voltage reference having their terminating regions electrically connected in series with one another between the circuit power supply interconnection and the voltage reference interconnection, and a threshold switch having first and second terminating regions and a control region by which that threshold switch is capable of being directed to provide a conductive path between threshold switch first and second terminating regions of a selected conductivity, the threshold switch first terminating region and control region each being electrically connected to a corresponding one of the voltage divider output and one of the voltage divider terminating regions and the threshold switch second terminating region being coupled through a switching circuit to the pass element control region so as to be capable of having the switching circuit switch the pass control element onto a nonconducting condition from previously selected conducting conditions upon sufficiently large voltages occurring between the circuit power supply and voltage reference interconnections.