Fast acting solid state circuit breaker

Claim 1

Means for interrupting the electrical current between a direct current source and a load when said current exceeds a predetermined value wherein said current interruption is accomplished wholly at solid state devices and without requiring the mechanical movement of elements, said source and said load each having positive and negative terminals, comprising: a sensing resistor connected between similar terminals of said source and said load, conductive means connecting the other terminals of said source and said load, a first transistor having an emitter collector circuit connected between said similar terminals of said source and said load in series relationship with said sensing resistor, said emitter collector circuit of said first transistor in series with said sensing resistor being the single current path between said similar terminals of said source and said load that is capable of transmitting significant operating current to said load whereby all significant current flow to said load is directly blocked by said first transistor at said emitter collector circuit thereof when said first transistor is made nonconductive, said first transistor having a base for controlling conduction through said emitter-collector circuit thereof, a second transistor having an emitter collector circuit connected between said first transistor base and said similar terminal of said load, said second transistor having a base for controlling conduction through said emitter-collector circuit thereof, a third transistor having an emitter-collector circuit connected between said similar terminal of said source and said second transistor base, said third transistor having a base for controlling conduction through said emitter-collector circuit thereof, a second resistor connected between said second transistor base and said other terminal of said source whereby a voltage rise is produced at said second transistor base when said third transistor becomes conductive, a pair of additional resistors series connected between said similar terminals of said source and said load, said pair of additional resistors having a circuit junction therebetween and conductive means connecting said third transistor base with said junction between said additional resistors to provide a voltage at said third transistor base which holds said third transistor non-conductive until said current exceeds said predetermined value, the increased voltage drop across said additional resistors accompanying said increase of current to said load above said predetermined value acting to turn said third transistor conductive and thereby turn said second transistor and said first transistor non-conductive with a regenerative feedback action.