Transient protection circuit

To protect a Class II integrated circuit bus from negative transients, the present invention uses a clamp circuit which is biased from the battery 55 and referenced to ground as opposed to being biased and referenced to ground. Thus, the current path is not from ground to the bus pin 22. Instead, it is from the battery through a blocking diode, a transistor, a resistor and a plurality of diodes to the bus pin yet referenced to ground. The transient protection circuit includes: a reference diode D5 with its cathode connected to ground; a transistor 65 biased as a current source having its output terminal operably connected to an anode of the reference diode; and at least a second diode D6 operably connected between the anode of the reference diode and a bus pin; whereby the transistor supplies current when a ground connection is intact. The arrangement is particularly suitable for use in a vehicle communication network.