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LAN interface with simplified overcurrent protection

  • US 5,548,467 A
  • Filed: 02/14/1994
  • Issued: 08/20/1996
  • Est. Priority Date: 02/14/1994
  • Status: Expired due to Fees
First Claim
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1. An overcurrent protection circuit comprising:

  • one input voltage terminal;

    a load terminal;

    a normally-on field-effect pass transistor and a sense resistor disposed in series between the input voltage terminal and the load terminal, the pass transistor being turned off by a voltage at a gate terminal;

    a transistor array having first, second, third and fourth terminals, and having the second terminal connected to the load terminal;

    a reference resistor connected between the first terminal of the transistor array and a point between the pass transistor and the sense resistor;

    means for providing a constant reference current through the reference resistor, the means disposed between the third terminal of the transistor array and ground;

    a resistor disposed to receive current flowing from the fourth terminal of the transistor array to ground;

    a resistor disposed between the input voltage terminal and the gate of the pass transistor; and

    one NPN transistor disposed for current sensing having an emitter terminal connected to ground, a base terminal connected to the resistor receiving current from the fourth terminal of the transistor array, and a collector terminal connected to apply a voltage to the gate terminal of the pass transistor so that when the current flowing from the fourth terminal of the transistor array to ground is substantially less than the constant current, the pass transistor is shut off.

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