Continuously Variable Active Reactance

Abstract

In this paper, circuits are described which produce continuously variable capacitive or inductive reactance. This is achieved by varying the duty cycle of a single switching device in parallel with a capacitor or in series with an inductor. Formulas are derived for the effective capacitance and inductance as functions of the duty cycle.An Active Variable Capacitance circuit was built and tested, and was shown to be fairly well described by the theoretical formulas. The Active Variable Capacitance is shown to have a practical application in the automatic tuning and current regulation of a wireless repeater resonator.