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New Piezoelectric Transformer Adapter with Universal Input Voltage Range

For the design of the AC-DC PT (Piezoelectric Transformer) adapter with a universal input voltage, it is important not only to find a solution to cover the wide range of input voltages but also to maintain control in the narrow switching frequency range. In general, PT efficiency is maximal near the peak gain point under the optimal load. As the operating frequency moves away from the peak gain point, the PT efficiency decreases due to the increase of the circulating current. In the half-bridge type circuit, which is widely used to implement an AC/DC PT adapter using PFM(Pulse Frequency Modulation), the above-mentioned problem exists if the universal input voltage specification is required. In this paper, a new circuit topology and control scheme for an AC-DC adapter with a universal input voltage range is proposed. Compared to the conventional half-bridge type, the proposed circuit has the following advantage. The range of the operating switching frequency is very narrow in spite of the universal input voltage variation(ac 90∼250Vrms) because the switch S1 with PWM control for line regulation and the switch S2 with PFM control for load regulation operate efficiency over the universal input voltage which is higher than the half-bridge type. Based on the analysis, as well as the simulation and experimental results provided in this paper, it is confirmed that the proposed circuit can be a good solution for the universal off-line input voltage specification.