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Power supply protection circuit

  • US 5,463,521 A
  • Filed: 06/03/1994
  • Issued: 10/31/1995
  • Est. Priority Date: 11/06/1992
  • Status: Expired due to Fees
First Claim
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1. An apparatus for protecting electronic circuit elements from hazardous voltages produced by an energy source, comprising:

  • a energy source for producing electrical energy having a predetermined energy level, said energy source having positive and negative terminals;

    an electrical load being connected to the positive and negative terminals of said electrical energy source, said electrical load receiving electrical energy from said energy source;

    a first Zener diode for receiving electrical energy from said electrical energy source and producing an overvoltage signal in response to receiving electrical energy greater than the breakdown voltage of the first Zener diode;

    an NMOSFET for controllably regulating the electrical current flowing through said electrical load, said NMOSFET having a drain, gate, source and substrate, and being connected between the negative terminal of said energy source and said electrical load; and

    control means for receiving the overvoltage signal and responsively limiting the NMOSFET gate-source voltage to increase the impedance of said NMOSFET to a predetermined impedance level, thereby limiting the current flowing through said electrical load to protect said electrical load from hazardous voltages, wherein said NMOSFET remains conducting to allow said electrical load to receive electrical energy from said energy source at substantially the breakdown voltage of said first Zener diode during a hazardous voltage condition.

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