Patent ID: 7619865

Claim:
A circuit protective device for an electrical system having a semiconductor output power switch, the circuit protective device comprising: an electronic current sensing circuit coupled to the power switch to provide a feedback signal representative of the current output I of the power switch; a threshold device which is responsive to the feedback signal exceeding a first presettable reference level to provide an overcurrent alert signal; a current generator that produces a signal representative of a functional relationship f(I) proportional to I 2 , based on the feedback signal, a function generating circuit that receives the overcurrent alert signal as an input and further receives an input from the current generator that generates the signal representative of the functional relationship f(I), the function generating circuit including an integration circuit coupled to the output of the current generator to provide a signal representative of the quantity f(I)*t, where t is the elapsed time following generation of the overcurrent alert signal; and further comprising a control circuit receiving an output of the integration circuit for providing a shut-down signal to disable the power switch when the output of the integration circuit exceeds a first threshold value, wherein the control circuit is operative to enable the power switch to turn back on after it has been turned off by the shutdown signal only when the output of the integration circuit falls below a second threshold value.