TDK has announced that TDK-Lambda UK’s power supply Power Factor Correction (PFC) controller patent application has been approved by the UK Intellectual Property Office.
The requirement for industrial power supplies to limit harmonic currents has existed for many years, and in Europe the standard is defined by EN 61000-3-2. Although power supplies that operate up to 100W can comply with the limits with a power factor of around 0.6, at higher power levels, a number close to unity is required.
Shaping the input current to be nearly sinusoidal is a common method to achieve compliance. The switching loss in a PFC circuit though, adversely affects efficiency.
For light loads, however, some level of cross-over distortion can be tolerated. Turning off the PFC circuit by controlling the conduction angle near the zero crossing point is acceptable and improves efficiency.
“We do this using a current reference that has lower harmonics than that achieved with traditional techniques like phase-cut, allowing a lower conduction angle for a given power to maximise efficiency,” explained Andrew Skinner, chief technology officer at TDK-Lambda EMEA.
TDK-Lambda’s patent utilises digital control to adjust the conduction angle and still maintain harmonic compliance across all loads. The control laws of the digital circuit can be changed depending on the level of harmonic compliance required, for example in LED lighting or computer equipment where the limits are more stringent.