Patent ID: 7324315

Claim:
A protection device connectable between an input and a load or connectable in a circuit, the device having a variable resistance circuit block connectable between the input and the load or connectable in the circuit as a series element, the circuit block having a first depletion mode FET, a second depletion mode FET having a gate coupled to the first FET with a gate of the first FET being coupled to the second FET, and a third depletion mode field effect transistor (FET) between the first and second FETs and having its conductive channel in series with conductive paths of the first and second FETS and said third FET for generating a negligible resistance when the current through the circuit block is below a threshold level and for generating a relatively high resistance when the current through the circuit block reaches the threshold level, further including a holding circuit between the first FET and the third FET providing a holding voltage for resetting the third FET after the occurrence of a transient without the need for an input voltage to the device having to return to zero or near zero, wherein the holding circuit consists of a fourth depletion mode FET with its conductive channel connected between the gate of the third depletion mode FET and the input and having its gate coupled to a location between the second depletion mode FET and the third depletion mode FET.