Comparison of single-switch driving circuits for piezoelectric transformer used in the back-light system

摘要

PT (Piezo-electric Transformer) has superior characteristics such as small and thin size, high voltage gain, high power density, and so on. This useful device is usually applied to the driving circuit of the back-light system of CCFL (Cold Cathode Fluorescent Lamp) for LCD (Liquid Crystal Displays) of Notebook PC or PDA(Personal Digital Assistants) because of the features mentioned above. As the driving circuit for PT built-in PDA, we are paying attention to a single-switch driving circuit, which is compact size. In this paper, three control methods for the driving circuit are compared and the suitable one for PDA use is chosen with the experiment. As a result, the frequency modulation with fixed off-duty is chosen and mentioned, and then the advantages of the method are clarified. It is also confirmed that the driving circuit with this method enables to obtain a stabilized AC 400V output and 82% power efficiency from DC 3V input under the conditions of the variations of load current or input voltage, from the experiments.