Overcurrent protection system

An improved overcurrent protection system having a power source of single or multi-phase ac, or dc, a load current sensing element for generating an overcurrent sensing voltage that is proportional to a load voltage across a load, a power switch for controlling the flow of load current, via a load current line connected to the load, an overcurrent sensing/inverse time delay circuit for sensing the overcurrent sensing voltage to generate an overcurrent fault signal in response to an overload condition, the overcurrent fault signal being generated sooner for heavier overloads and later for lighter overloads, and a logic circuit operative, under a normal load condition, to generate an input drive voltage at a drive circuit input line and under an overload condition, and in response to an overcurrent trip signal at its input, said logic circuit operates to turn-off the input drive voltage, wherein the improvement comprises:

• a drive circuit operatively connected at its input, via the drive circuit input line, to said logic circuit, operatively connected at a first output to said power switch and said overcurrent sensing/inverse time delay circuit, and operatively connected at a second output to said power switch, said drive circuit operating on the input drive voltage at its input to generate first and second drive voltages at the first and second outputs thereof;
• a drive circuit input current sensor operatively connected at its input to a third output of said drive circuit for generating a filtered voltage at its output that is proportionate to the voltage at its input;
• a trip signal detector operatively connected in its input to the output of said drive circuit input current sensor, and operatively connected at its output to the input of said logic circuit;
• and
• a crowbar circuit operatively connected to said overcurrent sensing/inverse time delay circuit, said power switch and said drive circuit, such that when the overload condition occurs, the corresponding increase in the overcurrent sensing voltage causes said overcurrent sensing/inverse time delay circuit at the appropriate time to generate the overcurrent fault signal causing said crowbar circuit to conduct, thereby causing the crowbarring of the first drive voltage across the first output of said drive circuit which causes said overcurrent sensing/inverse time delay circuit to turn-off, and due to the shorting of the first output of said drive circuit, a consequentual increase in the voltage at the input of said drive voltage input current sensor, this increase affecting a subsequent increase in the output voltage of said drive circuit input current sensor, as applied to the input of said trip signal detector, which generates an overcurrent trip signal at its output when the voltage at its input exceeds a threshold level, thereby causing said logic circuit to remove the input drive voltage to said drive circuit causing it to deactivate.