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Driving method and driving circuit for piezoelectric transformer, cold cathode tube emission device, liquid crystal panel and liquid crystal panel built-in apparatus
| Details |
Inventors: Takeda, Katsu; Nakatsuka, Hiroshi; Moritoki, Katsunori; Yamaguchi, Takeshi;
Assignee: Matsushita Electric Industrial Co., Ltd. (Kadoma, JP)
Primary Examiner: Budd; Mark O.
Assistant Examiner:
Attorney, Agent or Firm: Merchant & Gould P.C.
A driving method and a driving circuit for a piezoelectric transformer are capable of driving the piezoelectric transformer with high driving efficiency independently of an impedance change of a load such as a cold cathode tube by corresponding to the characteristic variance of the piezoelectric transformer, thereby also suppressing mechanical damage to be imposed on the piezoelectric transformer itself even if the load changes abruptly. The piezoelectric transformer is driven with a predetermined first frequency, and a power supply for a load connected to the secondary side of the piezoelectric transformer is started, and when an impedance of a load changes and reaches a predetermined impedance during the power supply, the driving frequency of the piezoelectric transformer is changed without a sweep from the first frequency to a predetermined second frequency. Furthermore, the second frequency is determined by detecting characteristics of the piezoelectric transformer before supplying the load steadily with electric power. |
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DETAILED DESCRIPTION The present invention is conceived in light of the aforementioned problems, and its object is to provide a driving method and a driving circuit for a piezoelectric transformer capable of driving the piezoelectric transformer with high driving efficiency independently of an impedance change of a load such as a cold cathode tube by corresponding to the characteristic variance of the piezoelectric transformer, thereby also suppressing mechanical damage that might be imposed on the piezoelectric transformer itself even if the load changes abruptly.
It is another object of the present invention to provide a cold cathode tube emission device that controls the emission of a cold cathode tube by the driving circuit of the piezoelectric transformer, a liquid crystal panel provided with this cold cathode tube emission device, and an apparatus provided with this liquid crystal panel such as a mobile telephone, a communication terminal etc.
To achieve the above object, a first method for driving a piezoelectric transformer according to the present invention is a method for driving a piezoelectric transformer having a primary side electrode and a secondary side electrode formed on a piezoelectric element, in which an AC voltage entering from the primary side electrode is converted and output from the secondary side electrode.
The method is characterized by the steps of driving the piezoelectric transformer with a predetermined first frequency, starting a power supply for a load connected to the secondary side of the piezoelectric transformer, and when an impedance of the load changes and reaches a predetermined impedance during the power supply, changing the driving frequency of the piezoelectric transformer from the first frequency without a sweep to a predetermined second frequency and driving the piezoelectric transformer.
To achieve the above object, a second method for driving a piezoelectric transformer according to the present invention is a method for driving a piezoelectric transformer having a primary side electrode and a secondary side electrode formed on a piezoelectric element, in which an AC voltage entering from the primary side electrode is converted and output from the secondary side electrode
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Ring Tones 
