LED Driver Power Factor Correction

The US Department of Energy (DOE) ENERGYSTAR™ solid-state lighting (SSL) specification requires that any power level must provide power factor correction (PFC). This standard applies to a range of specific products, such as recessed lights, cabinet lights and table lamps, where the power factor of LED drivers for residential applications must be greater than 0.7 and greater than 0.9 for commercial applications; however, this standard is voluntary. The EU's IEC61000-3-2 harmonic content standard specifies the total harmonic distortion performance of lighting applications with a power greater than 25 W, with a maximum limit equivalent to a total harmonic distortion (THD) < 35% and a power factor (PF) > 0.94. Although not all countries have an absolute mandate to improve power factor in lighting applications, some applications may have this requirement, such as utilities strongly promote the commercial application of products with high power factor in public facilities. In addition, when utilities purchase/maintain street lights, they can also decide whether to require high power factor (usually >0.95+) based on their wishes.

PFC technology includes passive PFC and active PFC. Passive PFC solutions are larger in size and require additional components to better change the current waveform, which can achieve a power factor of about 0.8 or higher. Among them, in lower power applications less than 5 W to 40 W, the flyback topology, which is almost the standard choice, only needs passive components and slight circuit changes to achieve a power factor higher than 0.7. Active PFC (see Figure 1) is usually added to the circuit as a dedicated power conversion stage to change the input current waveform. Active PFC usually provides boost, and the PFC output voltage range is up to 450 to 480 Vdc under a wide input range of 100 to 277 Vac. If the PFC stage is properly designed, it can provide high energy efficiency of 91% to 95%. However, with the addition of active PFC, a dedicated DC-DC conversion is still required to provide current stabilization.

Figure 1: Schematic diagram of active PFC application circuit