FC is an increasingly important issue for power supplies and loads; understand the different power-supply techniques used to implement it and their tradeoffs
| | By Steve Mappus, Systems Engineer, Fairchild Semiconductor Corp |  |
Power factor correction (PFC) is a growing and important issue in design of power supplies for non-resistive loads, driven by the increasingly complex loads of today's ubiquitous electronics, utility company requirements, and regulatory demands. This article looks at what it is and various approaches to achieving it in power-supply design. Equally important, it examines the tradeoffs among the various approaches, in terms of their performance, complexity, cost, and predictability. Power factor (PF) is one measure of power quality, indicating how efficiently energy is drawn from the
AC source. PF is defined as the ratio of real power in watts (W) to apparent power (product of root mean
square (RMS) current and RMS voltage) in voltŠamperes (VA).
Complex reactive loading introduces higher order current harmonics that distort the shape of the AC
current. This necessitates a more detailed definition of PF which takes into account current
displacement and harmonic distortion.
Equation (1) provides a definition of PF that accounts for current harmonic distortion, defined as
distortion factor in Equation (2), and phase displacement, defined as displacement factor in Equation (3). http://i.cmpnet.com/planetanalog/2009/07/C0420_edited.pdf
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