On 1 January 2001, the IEC 61000-3-2 regulation became effective. Since then, mitigating current harmonics has been essential to ensure that electronic equipment connected to single-phase power distribution lines conforms to electromagnetic compatibility directives. Today, high-quality rectification, commonly known as power factor correction (PFC), is a well-established technique widely adopted by the industry for powering various devices from the ac line. The topic has been studied by academia and industry since the mid-1980s; thus, an enormous amount of research has been published and countless solutions have been proposed since then. However, only a few of those solutions have encountered wide industrial usage. So, it is not the authors’ intention to provide a comprehensive review, but to take stock of the most used PFC techniques from an industry perspective. This paper will review the power factor theory with non-sinusoidal currents, the practical and regulatory aspects of using PFC, and the most common industry solutions for power factor correction in equipment operated from the single-phase, public, low-voltage supply system, with a special focus on boost PFC pre-regulators, their control methods, design procedures, and issues.

Nowadays, LED lamps have become a widespread solution in different lighting systems due to their high brightness, efficiency, long lifespan, high reliability and environmental friendliness. The choice of a proper LED driver circuit plays an important role, especially in terms of power quality. In fact, the driver controls its own input current in addition to the LED output current, thus it must guarantee a high power factor. Among the various LED drivers available on the market, the quasi-resonant (QR) flyback topology shows interesting benefits. This paper aims at investigating and analyzing the different issues related to the input current distortion in a QR flyback LED driver. Several effects, such as the distortion caused by the ringing current, crossover distortion due to transformer leakage inductance and crossover distortion due to the input storage capacitor have been experimentally reported. These effects, not previously studied for a high power factor (Hi-PF) QR flyback, have been analyzed in depth. Finally, some practical design guidelines for a Hi-PF QR flyback driver for LED applications are provided.

In a high-power factor quasi-resonant Flyback, an ideal zero current detection (ZCD) circuit and control circuitry enable the power switch turn-on in the exact instant a zero ringing current is reached after demagnetization. A nonzero current at the turn-on instant affects the input current shape and; consequently, affects its Total Harmonic Distortion (THD). This paper firstly deeply analyzes the effect on the distortion due to a nonideal ZCD circuit. After, some typical implementations of the ZCD circuit and their effect on the THD are analyzed, identifying their pros and cons. Finally, some experimental results are obtained to validate the analytical investigation.

The authors would like to make the following corrections to the originally published paper