A very simple control strategy for power factor correctors driving high-brightness light-emitting diodes

This paper presents a new control strategy for Power Factor Correctors (PFCs) used to drive High-Brightness Light- Emitting Diodes (HB-LEDs). This control strategy is extremely simple and it is based on the use of a conventional peak current- mode controller with a suitable selection of the compensation ramp waveform. In these conditions, an almost perfect sinusoidal line current is obtained at full load in the case of a topology based on the Boost converter. If the converter belongs to the Flyback family (Flyback, Buck-Boost, SEPIC, Cuk and Zeta), the line waveform appears notably distorted if the compensation ramp is a linear ramp, but becomes almost sinusoidal if the linear ramp is substituted by a properly chosen exponential waveform. The line waveform is slightly distorted when dimming control is implemented or when the converter works in either over-voltage or under-voltage conditions. However, the waveform maintains a very high Power Factor even in these conditions. Moreover, the line current is cycle-by-cycle controlled due to the peak current- mode control and, therefore, the input current feedback loop is extremely fast, thereby allowing this type of control to be used with high frequency lines (above 400 Hz).