Patent ID: 7362149

Claim:
A method of generating a sawtooth voltage ramp of period P/2 from an AC work voltage V IN having positive and negative half cycles that are not of the same length of time and whose sum is the period P, the method comprising the steps of: (a) converting V IN into a non-symmetrical square wave of period P and whose rising and falling edges correspond to zero crossings of V IN ; (b) detecting first direction edges of the non-symmetrical square wave of step (a) and indicating each detection with a first narrow pulse forming a sequence thereof having P as a period; (c) upon each first narrow pulse of step (b), starting from a selected voltage a first ramp voltage waveform whose change in voltage is in a selected direction, is linear with respect to time and continues until the next instance of this step; (d) removing any DC components of the first ramp voltage waveform to create a balanced ramp voltage that has equal regions of each polarity about zero volts, and whose opposing peak voltages are generally of equal magnitude; (e) detecting zero crossings in the balanced ramp voltage that are in the selected direction and indicating each detection with a second narrow pulse forming a sequence thereof having P as a period and whose occurrences are interleaved and P/2 in time between the sequence of first narrow pulses; (f) merging the first and second narrow pulses into one collection of phase symmetric zero crossing pulses of period P/2; and (g) upon each narrow pulse in the collection of phase symmetric zero crossing pulses of step (f), starting from another selected voltage a second ramp voltage waveform of period P/2, whose change in voltage is in another selected direction, is linear with respect to time and continues until the next pulse in the collection of phase symmetric zero crossing pulses of step (f).