Comparison of control concepts for off-line power supplies using piezoelectric transformers in class-E topology

Optimum control concepts have been studied at a 1 to 5 Watts wide-range off-line power supply demonstrator using a Transoner-type Piezoelectric Transformer. Using the class E topology it was demonstrated that the practicable control techniques are comparable in all resonant topologies, using a PI controller for different feed back methods to drive a VCO from the output voltage to be regulated. The ZVS or near-ZVS behavior during transient response, were achieved by duty-cycle tracking for optimum turn-on conditions in case of non-PLL control. In case of PLL-control, the load current turn-on synchronization of the switch delivers ZVS over the full operation range without trimming of the duty-cycle tracking. It was shown that a PI controller is sufficient in all cases to achieve transient response requirements of comparable hard-switching off-line power supplies as in fly-back topologies. The purpose of this work is to investigate an optimum concept for integrated circuit implementation as for an analog control IC.