Abdmct -At light load and/or high line, the peak-currentcontrolled boost power-factor corrector has considerable distortion. In this paper we determine the line-current waveform and the distortion of the conodor, the shape of the ideal reference signal, and discuss and analyze three distortion-reducing methods. The distortion-reducing methods are (1) adding a variable de offset to the sinusoidal reference, (2) predistorting the sinusoidal reference with a nonlinear network, and (3) converting the peak-current-control scheme into a simplified averagecurrentcontrol scheme. The paper presents analyses, practical considerations, and experimental results.
I. INTRODUCTIONThe peak-current-controlled boost power-fador corrector has several practical advantages over the averagecurrent-controlled boost correaor. Those advantages are:It is sufficient to sense only the switch Current.That can be accomplished with a current transformer, which improves efficiency. mere is no need for a arrent-error amplifier and its compensation network. Due to the low gain of the currentantrolling loop, input-filter oscillation is virtually non-existent. -?he corrector has a well-defined instantaneous pulse-by-pulse current Limit.A disadvantage is that considerable linearrent distortion is present under certain conditions. The distortion is caused by the non-negligible ripple current in the inductor and by the added stabilizing ramp. (The stabilizing ramp is required to avoid subharmonic instability above 50% duty ratio.) The distortion increases at high line voltage and light load. The distortion was first mentioned in [l], empirical distortion-reduction circuits were proposed in [1]33], Bacied on 'Reducing Distoction in PeakCurrentContmlled Boost Power-Factor Correcto~.," by R. Redl and B. P. Erisman, published in the and an approximate analysis of the line-current waveform was given in [4]. Until now, however, a detailed analysis of the waveform was not available. A purpose of this paper is to determine the line-current waveform and calculate the distortion in the case of a sinusoidal reference voltage. Another purpose is to determine the ideal reference waveform (the one which theoretically provides zero line-current distortion). A third purpose is to introduce three distortion-reducing techniques and present analyses and design guidelines for them. The distortion-reducing techniques to be presented in the paper are: (1) adding a variable dc o B e t to the sinusoidal reference, (2) predktorting the sinusoidal reference with a nonlinear circuit, and (3) converting the peakcurrent-control scheme into a simplified average-current-control scheme. By using any of the three techniques, it becomes possible to design economical, and at the same time lowdistortion, powerfactor arredors using the peak-current-controlled boost circuit.
II. ANALYSIS OF THE LINECURRENT WAVEFORM
A, SchematicFigure 1. Schematic of the boost power-factor corrector with peakcurrent control.
A primary-side controller @SC) using current mode PWM and an error signal isolator (ESI) using PAM have been developed by TOKO,
Inc.With over-current protection and slope compensation built in, the PSC boasts more features than its 8-pin rival, a 3842. The ESI, used with a bead-sized pulse transformer, replaces a TL43Uoptocoupler combination.
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