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Surge current protection circuit

  • US 4,091,434 A
  • Filed: 10/12/1976
  • Issued: 05/23/1978
  • Est. Priority Date: 10/16/1975
  • Status: Expired due to Term
First Claim
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1. A surge current protection circuit comprising an input terminal supplied with a rectified voltage, an output terminal to be connected to a load, a semiconductor controlled rectifier comprising gate, anode, and cathode electrodes, the anode and cathode electrodes being connected in series between said input and output terminals, and triggering means connected between said input and output terminals to supply a trigger voltage to the gate electrode of said semiconductor controlled rectifier, said triggering means comprising:

  • a first resistor connected in series between the gate and anode electrodes of said semiconductor controlled rectifier to supply a trigger voltage to said gate;

    a transistor having base, emitter, and collector electrodes, the collector and emitter electrodes of said transistor being connected in series between the gate and cathode electrodes of said semiconductor controlled rectifier; and

    biasing means comprising a series circuit connected between said input and output terminals for applying a bias voltage to the base electrode of said transistor, said series circuit comprising second and third resistors, said third resistor being connected between the base and emitter electrodes of said transistor, and said bias voltage across said third resistor being larger than the trigger voltage of said semiconductor controlled rectifier so as not to allow said semiconductor controlled rectifier to conduct when the voltage difference between said input and output terminals exceeds a predetermined value.

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