Murata Manufacturing Co., Ltd.

Kyoji Toshinari

Yasuyuki Morishima

Takashi Noma

A piezoelectric transformer inverter can be driven in wide ranges of input voltages and output currents so that a wide range of dimming can be achieved. Furthermore, the piezoelectric transformer inverter can maintain high efficiency in the overall driven ranges thereof so as to yield stable luminance. The above piezoelectric transformer inverter includes a piezoelectric transformer drive unit having conductive elements, switching elements, and a phase drive circuit to convert an inputted AC voltage into an AC voltage having a substantially constant frequency which is lower than the inputted AC voltage and output to a piezoelectric transformer, a phase-difference detecting unit for detecting the phase difference between a drive controlling signal of one of the switching elements and an output current or output voltage of the piezoelectric transformer to output a control voltage corresponding to the phase difference, and a frequency control circuit for outputting a pulse voltage signal of a frequency based on the control voltage to the phase drive circuit of the piezoelectric transformer drive unit.

Piezoelectric transformer inverter

A piezoelectric transformer inverter comprises: a piezoelectric transformer for performing voltage conversion of alternating voltage applied between primary electrodes to supply to a load connected to a secondary electrode; a driving-frequency control unit for controlling load current during driving of the load by changing the driving frequency of the piezoelectric transformer; a chopper unit for chopping input voltage applied into the driving-frequency control unit at a frequency of two or more times as high as the driving frequency and for controlling an average input voltage applied into the driving frequency control unit by changing a duty ratio of the chopping operation; and a dimming unit for intermittently stopping the driving frequency control unit by intermittently stopping the operation of the chopper unit at a frequency smaller than the driving frequency of the piezoelectric transformer, wherein even during a period in which the dimming unit is intermittently stopping the chopper unit, signals having a duty ratio for allowing the chopper unit to perform the chopping operation to be sustained inside the chopper unit.

A piezoelectric transformer-inverter in which a fluorescent light tube is light-modulated when a frequency controller changes the frequency of a drive voltage applied from a piezoelectric transformer drive circuit to a piezoelectric transformer in correspondence with a light-modulating voltage to thereby change the boost ratio of the piezoelectric transformer. A PWM inverter output variable circuit adjusts an average voltage supplied from a PWM inverter to a piezoelectric transformer drive circuit. When tube current is low, the average voltage is low, and when the tube current is high, the average voltage rises. Consequently, fluctuation in the drive frequency of the piezoelectric transformer is restricted even when the light-modulating voltage changes, making it possible to drive the piezoelectric transformer with a good boost ratio. Since the piezoelectric transformer is always driven close to its resonant frequency, there is almost no surge charge flowing to the transistor for driving the piezoelectric transformer.

Growing community of inventors

Kyoto, Japan

Kyoji Toshinari