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Power control circuit and a switching mode power supply employing this circuit

  • US 4,228,493 A
  • Filed: 12/21/1978
  • Issued: 10/14/1980
  • Est. Priority Date: 12/29/1977
  • Status: Expired due to Term
First Claim
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1. A power control circuit for controlling the base current to a switching transistor connected in series with a primary winding of a switching transformer comprising:

  • first means for detecting the current flow through said transistor and producing a first signal when said current flow exceeds a first predetermined value;

    second means for detecting the current flow through a secondary winding of said transformer and producing a second signal when current flow through said second winding exceeds a second predetermined value;

    means for generating a sawtooth waveform and comparing said waveform to a reference voltage to produce a sequence of timing pulses;

    first amplifier means for supplying base current to said switching transistor;

    second amplifier means for absorbing base current from said switching transistor, said base current being cyclically supplied to and absorbed from said transistor;

    logic means connected to said first and second detecting means, said generating and comparing means and said first and second amplifier means for controlling supplying of base current to and absorbing current from said switching transistor in accordance with said pulses and said first and second signals.

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