The circuits on this page operates at line voltage which is killing dangerous. The connections and experiments of the circuits belong to a professional electrician or a amateur which has experiences enought.
Everyone who practices these circuits make it with his/her own risk. The author of this page take no liability for damages which can happen.

The idea is opposite of typical motor frequency convertor where the main voltage is first rectified and later chopped to a variable frequency. Outputting voltage must be in proportion of frequency. The lower the frequency the lower the voltage must be.

This simple circuit is operating as a cycloconverter. It picks every 3th half wave of  the inputting main voltage. The result is 1/3th from the frequency and even  from the voltage. It is near ideal and comparable to the normal motor frequency convertor. Only limitation is the speed control. This is not stepless but usable speeds are 1/3th, 1/5th, 1/7th and so on from the mains freq.

This circuit is dimensioned to the 1/3 frequency division. Increasing time constant of R2C1 it can operate in more lower speeds.