Method and apparatus for measurement of AC voltage signal at light load operation

The present invention puts forward a method and an apparatus for measurement of an AC voltage signal at light load operation. An observation is made that the peak voltage value for a rectified AC voltage signal is substantially the same from cycle to cycle. Using this observation, a method of measuring an AC voltage is used to determine a more accurate RMS voltage value under light load conditions. The method includes rectifying the AC voltage signal to form a rectified signal, sampling the rectified signal to obtain a set of sampled values for each half-cycle of the AC voltage signal, searching the sampled values for each half-cycle to determine a local minimum value for each half-cycle, searching the sampled values following the local minimum value to determine a local maximum value for each half-cycle, and calculating a root mean square value from the local maximum value for each half-cycle thereby determining the root mean square value for each half-cycle of the AC voltage signal.