Constant current circuit

  • US 7,944,272 B2
  • Filed: 09/29/2009
  • Issued: 05/17/2011
  • Est. Priority Date: 09/29/2008
  • Status: Active Grant
First Claim
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1. A constant current circuit comprising:

  • a temperature compensation circuit configured to output a first current which is temperature-compensated; and

    a current supply circuit configured to supply a second current to the temperature compensation circuit,the temperature compensation circuit including;

    a voltage multiplication circuit including a first transistor configured to generate a base-collector voltage obtained by multiplying a base-emitter voltage by a predetermined ratio;

    a second transistor identical in conductivity type and substantially equal in base-emitter voltage to the first transistor;

    a first resistor having one end connected to a collector of the first transistor and the other end connected to a base of the second transistor; and

    a second resistor having one end connected to an emitter of the first transistor and the other end connected to an emitter of the second transistor,the first current being output according to a collector current of the second transistor, andthe second current being supplied to a connection point between the base of the second transistor and the first resistor, to generate between both ends of the first resistor a voltage varying substantially in proportion to temperature,the current supply circuit including;

    a third transistor and a fourth transistor whose emitter areas are different from each other; and

    a fifth resistor whose temperature coefficient is substantially equal to a temperature coefficient of the first resistor, the fifth resistor having both ends applied with a differential voltage between a base-emitter voltage of the third transistor and a base-emitter voltage of the fourth transistor,wherein the second current is supplied according to a current flowing through the fifth resistor.

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