Zero crossings for a non-symmetrical V.sub.IN may be determined by first amplifying and clipping V.sub.IN to create a non-symmetrical square wave whose zero crossings are those of V.sub.IN. A selected polarity edge of the non-symmetrical square wave may be taken as a 0.degree. indicator and is used to create a fundamental sawtooth ramp of the same frequency and in phase with V.sub.IN. The fundamental sawtooth ramp starts at zero volts, linearly ramps to some peak and is AC coupled to a comparator whose other input is zero volts. That creates a square wave that is symmetrical as to its half-cycles, and whose every other edge is synchronous with the start of the fundamental sawtooth ramp, and whose intervening edges occur in the middle of the ramp. The intervening edge is detected and taken as a 180.degree. indicator. The 0.degree. indicator and the 180.degree. indicator can be merged into a combined signal that may be used to initiate synchronous rectification as well as to create a utility sawtooth ramp at twice the rate of the fundamental sawtooth ramp and whose amplitude may also be controlled. The fundamental ramp can be used to create an arbitrary number of selectedly placed pulses indicative of a desired division of the period of a cycle for V.sub.IN by first creating a steady voltage proportional to the peak voltage of the fundamental ramp, and then comparing proportional occurrences of that fundamental ramp to thresholds that are selected percentages of the steady voltage proportional to the peak voltage.