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Power Factor Correction with AC Side Passive Elements

IP.com Disclosure Number: IPCOM000109506D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 2 page(s) / 82K

Publishing Venue

IBM

Related People

Carlsten, R: AUTHOR

Abstract

A parallel resonant circuit is inserted before the normal bridge rectifier and filter capacitor of the input section of a switching power supply (see Fig. 1). The resultant circuit improves the power factor of the power supply and greatly reduces the peak current of the AC input by lengthening the current conduction time. A number of circuits already exists for doing power factor correction and input current wave shaping on the input of switching power supplies. Generally these circuits are designed for power supplies above the 250-watt output range. In these circuits both active and passive components are used to develop a Boost converter that boosts the input AC to a DC voltage that is above the peak of the AC level. This invention is designed for use in those supplies that are under the 250-watt output range.

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Power Factor Correction with AC Side Passive Elements

       A parallel resonant circuit is inserted before the normal
bridge rectifier and filter capacitor of the input section of a
switching power supply (see Fig. 1).  The resultant circuit improves
the power factor of the power supply and greatly reduces the peak
current of the AC input by lengthening the current conduction time.
A number of circuits already exists for doing power factor correction
and input current wave shaping on the input of switching power
supplies.  Generally these circuits are designed for power supplies
above the 250-watt output range.  In these circuits both active and
passive components are used to develop a Boost converter that boosts
the input AC to a DC voltage that is above the peak of the AC
level. This invention is designed for use in those supplies that are
under the 250-watt output range.  It uses only two components, an
inductor and a capacitor, compared to the Boost method that has a
large component count.

      The parallel resonant circuit is tuned to the first of the odd
harmonic frequency seen on the primary side.  The harmonics on the AC
side are odd harmonics of the 60 Hz., so the resonant frequency is
set to 180 Hz. (3th harmonic).  Fig. 1 shows the circuit and AC input
current waveform.  Note that the conduction time of the current
waveform is much longer than the typical bridge rectifier circuit;
also the peak current is much less.  Fig. 2 shows the Bode plot...