Electricity: electrical systems and devices – Electrostatic capacitors – Fixed capacitor
Reexamination Certificate
1999-11-17
2001-10-16
Reichard, Dean A. (Department: 2831)
Electricity: electrical systems and devices
Electrostatic capacitors
Fixed capacitor
C361S321200, C361S320000, C361S321400, C361S306300
Reexamination Certificate
active
06304425
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a circuit board having thereon coupled multilayered ceramic capacitors capable of reducing generation of sounds caused by piezoelectric effects and a method for mounting the multilayered ceramic capacitors on the circuit board.
DESCRIPTION OF THE PRIOR ART
Aluminum electrolysis capacitors had been widely used as power smoothing capacitors in smoothing circuits of such power supply circuits as DC—DC converters and the like.
However, as the sizes of electronic circuits and devices were scaled down, tantalum electrolysis capacitors, a smaller tantalum electrolysis capacitor being capable of providing a capacitance level obtainable from a larger aluminum electrolysis capacitor, were employed in electronic circuits, e.g., smoothing circuits of power supply circuits, requiring large capacitance.
And, as the electronic circuits and devices are further miniaturized while requiring less power consumption, most of the conventional capacitors employed therein have been rapidly replaced by multilayered ceramic capacitors.
The use of multilayered ceramic capacitors have been rapidly extended since they are small but have excellent reliability and durability.
Since, however, a dielectric material being used in a multilayered ceramic capacitors having a small size but with large capacitance is of the type having a large dielectric constant, vibrations are generated due to piezoelectric effects when AC currents are applied thereto along with DC currents. The vibrations thus generated tend to become stronger as the dielectric constant of the dielectric material becomes greater and the size of the capacitor becomes larger.
Multilayered ceramic capacitors having relatively large sizes and large capacitance are normally employed in the smoothing circuits of the power supply circuits, resulting in such vibrations occurring frequently.
Furthermore, once the vibrations are generated in the multilayered ceramic capacitors as described above, the vibrations of the capacitors are transferred to the circuit board on which the capacitors are mounted; and, therefore, in some cases the circuit board resonates with the vibrations so that sounds can be amplified. That is to say, the vibrations of the capacitors result in the vibration of the surrounding air to produce audible sounds and, at the same time, cause the resonant vibrations of the circuit board to occur. Consequently, sound pressure levels increase, which in turn results in harsh audible sounds being produced.
SUMMARY OF THE INVENTION
It is, therefore, an object of the present invention to provide a circuit board capable of reducing audible sounds generated by piezoelectric effects and a method for mounting multilayered ceramic capacitors on the circuit board.
In accordance with one aspect of the present invention, there is provided a circuit board having an electronic circuit formed thereon, the electronic circuit including a pair of multilayered ceramic capacitors, wherein each of the capacitors includes a body having dielectric layers formed of a dielectric ceramic material and internal electrode layers and a pair of external terminal electrodes formed on two sides of the body, the body being of a substantially hexahedral shape, the dielectric layers and the internal electrode layers being stacked alternately in the body and the internal electrode layers being connected in parallel to the external terminal electrodes in an alternate manner, characterized in that:
the capacitors are disposed at substantially plane-symmetrical positions on two opposite surfaces of the circuit board and substantially identical voltages are applied to the capacitors,
wherein the electronic circuit is of a type in which voltages applied to the capacitors have frequencies varying in an audible frequency band.
REFERENCES:
patent: 5095402 (1992-03-01), Hernandez et al.
patent: 5157582 (1992-10-01), Sugita et al.
patent: 5493769 (1996-02-01), Sakai et al.
patent: 5604328 (1997-02-01), Kubota et al.
patent: 5889445 (1999-03-01), Ritter et al.
patent: 6054754 (2000-04-01), Bissey
patent: 6060954 (2000-05-01), Liu et al.
Ha Nguyen
Reichard Dean A.
Rosenman & Colin LLP
Taiyo Yuden Co. Ltd.
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