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Flyback power converter having a constant voltage and a constant current output under primary-side PWM control

  • US 6,862,194 B2
  • Filed: 06/18/2003
  • Issued: 03/01/2005
  • Est. Priority Date: 06/18/2003
  • Status: Expired due to Fees
First Claim
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1. A flyback power converter, comprising:

  • a transformer having a secondary winding, a first primary winding, and a second primary winding, said first primary winding and said second primary winding each having a first terminal and a second terminal respectively, wherein said second terminal of said first primary winding is connected to said first terminal of said second primary winding, wherein said second terminal of said second primary winding is connected to a ground reference;

    an output rectifier connected from said secondary winding to an output of the flyback power converter;

    a switching transistor for controlling the voltage across the primary windings of the flyback power converter, wherein a drain of said switching transistor is connected to an input of the flyback power converter;

    a current-sense resistor for generating a current-sense voltage, wherein said current-sense resistor is connected between a source of said switching transistor and said first terminal of said first primary winding;

    a PWM controller for providing a PWM signal to drive a gate of said switching transistor, wherein said PWM controller has a VCC input for receiving power, a detection input for receiving a flyback voltage, a current-sense input for current detection, and a GND input connected to the first terminal of said first primary winding, wherein said current-sense input is connected to said source of said switching transistor;

    a power-pin capacitor for starting up said PWM controller, wherein said power-pin capacitor is connected between said VCC input and said GND input of said PWM controller;

    a start-up resistor for charging said power-pin capacitor, wherein said start-up resistor is connected from the input of the power converter to said VCC input of said PWM controller;

    a power-pin diode connected from said second terminal of said first primary winding to said VCC input of said PWM controller;

    a detection resistor for receiving a bias current to compensate for the voltage drop across said output rectifier, wherein said detection resistor is connected from said second terminal of said first primary winding to said detection input of said PWM controller;

    a transit-voltage suppressor connected in parallel with said second primary winding; and

    a snubber diode connected in series with said transit-voltage suppressor.

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