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Control arrangement for a switch mode power supply

  • US 4,942,509 A
  • Filed: 03/28/1989
  • Issued: 07/17/1990
  • Est. Priority Date: 01/11/1988
  • Status: Expired due to Term
First Claim
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1. A control arrangement for interfacing a main converter in a switched mode power supply with a full wave rectified mains power supply, the control arrangement receiving an average input voltage Vi having a rectified sinusoidal waveform from the rectified mains supply and providing an average output d.c. voltage Vo as the input to the main converter, and comprising a voltage converter having an inductance, a switching means to connect the inductance across said input voltage, and a control means determining the average input current I to the voltage converter and operable to control a switching duty ratio D of the switching means in dependence thereon, wherein the voltage converter has a voltage transfer function which is a function f(D) of the duty ratio, and said control means is arranged so that f(D) is substantially inversely proportional to I so that the average input current has substantially the same waveform as said average input voltage.

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