Metal working – Method of mechanical manufacture – Electrical device making
Reexamination Certificate
2000-01-24
2001-11-20
Young, Lee (Department: 3729)
Metal working
Method of mechanical manufacture
Electrical device making
C029S606000, C029S609000, C029S852000, C029S854000, C029S855000, C333S181000, C333S184000, C333S185000, C336S200000, C336S232000
Reexamination Certificate
active
06317965
ABSTRACT:
FIELD OF THE INVENTION
The present invention generally relates to noise-cut filters for power converters, and in particular to noise-cut filters for filtering switching noises that occur upon switching operations of semiconductor switching devices that constitute a power converter, such as an inverter.
BACKGROUND OF THE INVENTION
Semiconductor switching devices of a power converter, such as an inverter, perform switching operations based on drive signals which undergo pulse width modulation (PWM) with the carrier frequency being in the range of several KHz to about twenty KHz. During the switching operations, switching noises having frequency components of several dozens of KHz are generated from the power converter.
Of the frequency components of the switching noises as described above, those components having a frequency of one hundred KHz or higher have adverse influences on external equipment. In view of this situation, various legal regulations have been laid on power converters in recent years, in an attempt to reduce or eliminate such adverse influences. To deal with the regulations, the power converters are equipped with suitable noise-cut filters.
A known example of noise-cut filter for a power converter includes a single reactor in which an electric wire is wound around a core formed of, for example, ferrite, amorphous alloy, or crystalline alloy, and a single condenser in the form of a film or a chip. The reactor and the condenser are coupled into an inverted L-shape, to provide a filter for filtering switching noises that occur upon switching operations of semiconductor switching device of the power converter.
As one of the prior-art references concerning noise-cut filters for power converters, “Integrated Output Filter and Diode Snubber for Switchmode Power Converters”, IEEE, 1994, pp. 1240-1245 discloses a filter circuit having an integrated, flat-sheet structure including a rectifier, RC snubber circuit, and an LC filter circuit. This reference also provides explanation of basic methods for manufacturing the respective circuits.
In addition, “Integrated Filters For Switch-Mode Power Supplies”, IEEE, 1995, pp. 809-816 as another prior-art reference discloses three types of LC filter circuits having difference structures depending upon dielectric materials used therein. Namely, the dielectric materials are classified into those having a ceramic structure, and those having a non-ceramic structure, and one type of filter circuit (using BaTiO
3
as dielectric material) having a flat-sheet structure is proposed as of a type using a ceramic material as a dielectric, while two types of filter circuits (sheet type, and vapor deposition type using plasma) having a film-like structure are proposed as of a type using a non-ceramic material as a dielectric.
The reactor used in the above-described known type of noise-cut filter generally has a toroidal shape, and the capacitor is a pin-inserted type and has a flat shape or a cylindrical shape. Where the reactor and capacitor are mounted on a printed board inside the power converter, a space required for mounting these components will be greater than the sum of the volumes of the respective components, resulting in a reduced assembling efficiency. Where this type of noise-cut filter is mounted on the printed board by separate wiring, the number of coupling portions will be increased, and the manner of fixing the individual components will be undesirably complicated.
A so-called composite LC filter of a chip type or pin-inserted type, which is commercially available and includes a composite unit of inductor and capacitor, has a cut-off frequency of several MHz or higher, whereas the cut-off frequency normally required to filter switching noises occurring upon switching operations of semiconductor switching devices is as low as about 150 KHz, for example. Thus, the commercially available filters are unable to filter the switching noises occurring upon switching operations of the semiconductor switching devices.
Furthermore, in a power converter such as an inverter, several amperes of current is desired or required to flow through a noise-cut filter used for the converter. It is thus difficult to employ the commercially available composite LC filter as the noise-cut filter, in view of the current capacity and the cost.
The filter circuits disclosed in the above-identified two prior-art references have problems of complicated manufacturing methods, which make the circuits unsuitable for practical use and result in increased manufacturing cost.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a noise-cut filter which is able to deal with low-frequency noises, while assuring a sufficiently large current capacity.
It is another object of the invention to provide a small-sized, inexpensive noise-cur filter having an excellent operating reliability, which filter is fabricated by a simple manufacturing method in which suitable circuit patterns can be easily mounted on a substrate.
To accomplish the first object, a noise-cut filter is provided which includes: a first dielectric sheet; first and second spiral coil patterns formed on opposite surfaces of the first dielectric sheet, respectively, such that the first and second spiral coil patterns are aligned with each other in a direction perpendicular to a plane of the first dielectric sheet, the first and second spiral coil patterns being formed from a conductive paste; a first main circuit pattern having a function of inductors and formed by bonding a first main circuit conductor to the first spiral coil pattern formed on one of the opposite surfaces of the first dielectric sheet, the conductor being formed by stamping with a punch press so that the conductor has a cross sectional area large enough to allow a desired level of current to flow therethrough, and has substantially the same shape as the first spiral coil pattern; a first grounding wire connected to the second spiral coil pattern formed on the other surface of the first dielectric sheet remote from the firs main circuit pattern, the first grounding wire leading a current involving noises which flows from the first main circuit pattern into the second spiral coil pattern via the first dielectric sheet having a function of capacitors, to a ground terminal; a second dielectric sheet formed in the shape of a flat sheet; third and fourth spiral coil patterns formed on opposite surfaces of the second dielectric sheet, respectively, such that the third and fourth spiral coil patterns are aligned with each other in a direction perpendicular to a plane of the second dielectric sheet, the third and fourth spiral coil patterns being formed from a conductive paste; a second main circuit pattern having a function of inductors and formed by bonding a second main circuit conductor to the third spiral coil patter formed on one of the opposite surfaces of the second dielectric sheet, the conductor being formed by stamping with a punch press so that the conductor has a cross sectional area large enough to allow a desired level of current to flow therethrough, and has substantially the same shape as the third spiral coil pattern; a second grounding wire bonded to the fourth spiral coil pattern formed on the other surface of the second dielectric sheet remote from the second main circuit pattern, the second grounding wire leading a current involving noises which flows from the second main circuit pattern into the fourth spiral coil pattern via the second dielectric sheet having a function of capacitors, to a ground terminal; and an insulating sheet formed in the shape of a flat sheet, which is interposed between the first dielectric sheet carrying the first main circuit pattern and the first grounding wire, and the second dielectric sheet carrying the second main circuit pattern and the second grounding wire thereon; wherein one of opposite ends of the first main circuit conductor is connected to one of opposite ends of the second main circuit conductor, such that the other ends of the first and second main
Aihara Takashi
Fukasawa Naoto
Maeda Takao
Matsumoto Yoshihiro
Okamoto Kenji
Fuji Electric & Co., Ltd.
Kim Paul
Rossi & Associates
Young Lee
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