Patent ID: 8570697

Claim:
Apparatus for protecting a signal line bus driver from overvoltage faults comprising: a first solid-state switch having a first gate to control an opening and a closing of the first solid-state switch and configured to block current having a positive voltage when open; a second solid-state switch configured to block current having a negative voltage when open having a second gate to control an opening and a closing of the second solid-state switch and; a comparator circuit connected to: receive bus driver output voltage from the bus driver; receive a reference voltage that has a magnitude that exceeds bus driver output voltage by a predetermined magnitude; and produce a comparator output signal responsively to a fault-induced voltage in a signal line that has a magnitude that exceeds the reference voltage, the first and second switches being connected in series with one another, being connected in series with the bus driver, being interposed between the bus driver and an output end of the signal line and being connected so that at least one of the solid-state switches opens responsively to the comparator output signal; a constant current source coupled with the gates of the first and second solid-state switches; and a cut-off switch interposed between the constant current source and the signal line, the cut-off switch configured to close in response to the comparator output signal so that the first and second solid-state switches open in responsive to closing of the cut-off switch.