This paper presents a new, simple and cost effective solution for the power factor correction of the input current of a switch mode power supply, which meets the IEC limits on harmonic distortion. A sloped air-gap inductor, which adapts its inductance values to the input current conditions of the power supply, is used to shape the current to comply with the limits for harmonic distortions as defined in EN61000-3-2. It is shown that using a classical inductor design, the filter inductor is too bulky, whereas the volume of the sloped air-gap choke is as small as the switching transformer of the power (e.g. 100 kHz) supply, In fact, the volume required is no bigger than that required for an active PFC circuit, but at a fraction of the cost.
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