Driving LEDs
Upon the input voltage source, several topologies can be used to drive LEDs. These range from standard Linear Current Source with simple ballast resistor to limit current, to switching technology, of which there are three main types: "Buck" when output voltage applied to LEDs is systematically lower than the input voltage, "Boost" in the reverse case, and "SEPIC" when both cases can apply.
Another issue is the Power Factor Correction. IEC 1000-3-2 standards set regulations to limit the harmonics injected into the AC line. Specifically for lighting applications, these apply if the input power is greather than 25W (Clas C). In addition, in some jurisdictions even if formal IEC compliance is not required, a minimum power factor may be required in these applications.
This text is an abstract of the ON Semiconductor "LED Driver Solutions" manual.
