UK Intellectual Property Office approves PFC controller

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. A common method used to achieve compliance is by shaping the input current to be nearly sinusoidal. However, the switching loss in a PFC circuit adversely affects efficiency. For light loads, however, some level of cross-over distortion can be tolerated. By controlling the conduction angle near the zero crossing point, the PFC circuit can be turned off and efficiency improved.

To adjust the conduction angle while maintaining harmonic compliance across all loads, TDK-Lambda’s patent utilises digital control. Depending on the level of harmonic compliance required, the control laws of the digital circuit can be changed.

“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,” commented Andrew Skinner, Chief Technology Officer, TDK-Lambda EMEA.