Tokin Corporation

Hutoshi Shiotani

Yoshihiro Ino

Katsunori Kumasaka

Tetsuo Yoshida

Yoshiaki Fuda

Naoki Wako

Hiroyuki Satoh

In an inverter circuit including a piezoelectric transformer (17) for supplying a voltage signal to a cold-cathode tube (50), a driver (12) for driving the piezoelectric transformer, a voltage-controlled oscillator (11) for producing an oscillation pulse voltage signal having an oscillation frequency controlled by a control voltage, a phase difference detection circuit (15) for detecting as a detected phase difference a phase difference between input and output voltage signals of the piezoelectric transformer, and a control circuit (16) for producing the control voltage so that the detected phase difference is coincident with a predetermined value, a current detection circuit (21) detects as a detected current value a current which flows through the cold-cathode tube. Supplied with the oscillation pulse voltage signal and the detected current value, a power control section (22) controls an electric power of the oscillation pulse voltage signal so that the detected current value has a preselected value. The power control section produces a power-controlled pulse voltage signal and supplies the power-controlled pulse voltage signal to the driver.

Inverter circuit for lighting a cold cathode tube by the use of a

A piezoelectric transformer comprising a rectangular plate of a piezoelectric material which is polarized in a thickness direction in a first half section of the plate in a longitudinal direction but is polarized in a width direction in a second half section of the remaining half section. A pair of primary electrodes are coated on the upper and the lower surfaces of the first half section and a pair of secondary electrodes are coated on the opposite side surfaces of the second half section, in an alternative structure, the plate is polarized in the thickness direction in opposite end sections of the plate having a size one third of length of the plate and polarized in width direction at the remaining middle section of plate between opposite end sections. The pair of primary electrodes formed on upper and lower surfaces of opposite end sections of plate and pair of secondary electrodes formed on opposite side surfaces of middle section. The pair of secondary electrodes may be deposited on upper or lower surfaces adjacent opposite side edges. In a voltage converter using the piezoelectric transformer, a pulse generator generates two voltage pulse signals having frequency equal to resonance frequency of transformer but being reverse to each other in phase, which signals are applied to primary electrodes, respectively to produce high voltage AC output across secondary electrodes isolated from primary electrodes.

Voltage converter for use with a piezoelectric transformer

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Miyagi, Japan

Hutoshi Shiotani