What are PF and PFC and why are they important in specifying LED drivers ?
A: The power factor of a power supply is a ratio of the real power to apparent power of the power consumed by the supply. It is expressed either as a number between 0 and 1 or as a percentage between 0 and 100%.
Real power is the actual power drawn by the supply, whereas apparent power is the product of the input current and the input voltage. Since voltage and current may be out of phase in non-linear loads such as switch mode power supplies, this product can be much greater than real power.
In order to maintain a high power factor, many power supplies (including LED power supplies) must employ some form of power factor correction (PFC) whose role is to ensure that the input current waveform matches in the input voltage waveform as closely as possible in both waveform shape and phase.
A high power factor is required because a power supply with low power factor will draw more current for a given power consumption than a supply with high power factor. That means that a low power factor supply will result in greater power losses in all transmission lines and a large number of low power factor loads may even require a resizing of these utility lines. There are a number of standards now in effect requiring certain minimum levels of power factor in power supplies, including LED drivers.