A simple inductorless AC-line voltage autotransformer

A very simple AC-line voltage autotransformer based on switched capacitors (SC) is presented. Compared to classical autotransformers or various AC voltage stabilisers it is lightweight and small. Various configurations for SC-autotransformers and possible different switching algorithms are pointed out. The theoretical background for the simplest SC-autotransformer is developed from basic circuit theory. Its characteristics are investigated mathematically and numerically. Designer´s guidelines are deduced and a prototype SC-autotransformer is designed. The autotransformer and minimum control circuitry for its operation are constructed, and the basic characteristics are measured. The theoretical and measured waveforms agree very well. By controlling the charging/discharging intervals of the capacitors-the output voltage is controlled. A special characteristic of the simplest SC-autotransformer is its capability to operate either in step-up or step-down mode using the same configuration