Resonant current estimation and phase-locked loop feedback design for piezoelectric transformer-based power supplies

A control system to achieve zero-voltage switching (ZVS) for an inductorless half-bridge piezoelectric transformer-based resonant power supply is presented. Both the phase and frequency of the resonant current are locked to the switching waveform using an analogue phase-locked loop (PLL) to ensure ZVS operation. We present two resonant current estimation circuits which generate the reference signals for the PLL. We also present three PLL feedback designs to produce the in-phase gate drive signals with adequate deadtime. The operating principle of the control system and its ability to achieve ZVS operation is discussed. Experimental results of the PLL circuit verify the successful operation of the proposed system. The six permutations of current estimation and feedback are contrasted and conclusions for application-specific usage are made.