Consideration of a single-switch inverter for piezoelectric transformer with a new control method

A driving inverter circuit for piezoelectric transformer (PT) with a new control method is proposed and the simulation and the experimental results are revealed. The most appropriate drive circuit is presented for back-light system of cold cathode fluorescent lamp (CCFL), which is used in liquid crystal displays (LCD) for portable devices such as notebook type PC or personal digital assistants (PDA). The circuit has the features such as compact-size, lightweight, high voltage gain, high power efficiency, satisfactory dynamic characteristics and low harmonic distortion of the output. The pulse frequency modulation (PFM) with fixed off-time of the switch is employed as the control method. It realizes both of stabilizing and dimmer controls of CCFL with only a single simple control circuit. It is confirmed from the experiments that the driving inverter with this method enables to realize a stabilized AC 400 V output and 82% power efficiency from DC 3 V input under the conditions of the variations of load current and/or input voltage, that the dynamic characteristic are improved by the well-suited low quality factor (Q) of the circuit. Also, it is revealed that the dimmer control can be performed with 80% or more power efficiency, and furthermore that the excellent dynamic characteristics are realized using the suitable low Q of the circuit.