Electricity: measuring and testing – Measuring – testing – or sensing electricity – per se – Magnetic saturation
Reexamination Certificate
2000-11-16
2002-10-08
Le, N. (Department: 2858)
Electricity: measuring and testing
Measuring, testing, or sensing electricity, per se
Magnetic saturation
Reexamination Certificate
active
06462531
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to current detectors, particularly to that utilizing a Hall-effect device for obtaining a voltage proportional to the magnitude of the current detected.
By the term “Hall-effect device” used herein and in the claims appended hereto is meant the voltage generator built on the familiar Hall effect to give an output voltage in direct proportion to the magnetic field applied. Disposed on a current path, the Hall-effect device will be subjected to the magnetic field that is generated in proportion to the magnitude of the current flowing through the path. The result will be the production of a voltage proportional to the current magnitude.
The instant applicant proposed in U.S. patent application Ser. No. 09/555,361, filed May 30, 2000, to create an insulating film over a Hall-effect device formed in a semiconductor substrate and, on this insulating film, a conductor layer for carrying a current to be detected. The current path is thus situated as close as feasible to the Hall-effect device, resulting in enhancement of the current-detecting sensitivity.
This prior art current detector proved to be unsatisfactory, however, in the magnitude of the current that can be carried by the conductor ductor layer. A current of, say, one hundred amperes or more could not possibly be made to flow through it.
The applicant attempted to defeat this shortcoming of the prior art device by developing a current detector in which two printed-on current paths are formed on a circuit board, one of them being electrically connected to a Hall-effect device. The magnitude of the current flowing through the other current path is detectable from that of the current flowing through the one current path, only if the resistance values of both current paths are known. Variations in the current magnitude are likewise detectable.
This improved prior art device has proved to have its own weakness: The two current paths must of necessity be so spaced from each other that an inconveniently great temperature difference tends to occur therebetween. Such a temperature difference is undesirable because it can bring about fluctuations in the ratio at which the current is divided between the two paths, with the consequent deterioration of the accuracy of current detection.
SUMMARY OF THE INVENTION
The present invention aims at the provision of a current detector of the type incorporating a Hall-effect device, that is capable of more accurately detecting a current of greater magnitude than heretofore.
Briefly, the current detector according to the invention comprises a Hall-effect device for generating a voltage proportional to magnetic field strength, a first and a second current path terminal for the flow of a current to be detected or measured, and first and second conductor means connected between the first and the second current path terminal for providing a first and a second current path, respectively, therebetween. The first and the second conductor means have their resistances predetermined in relation to each other so that the current on the first current path terminal is divided at a predetermined ratio into a first fraction flowing through the first conductor means to the second current path terminal, and a second fraction flowing through the second conductor means to the second current path terminal. A conductor included in the second conductor means is so arranged in relation to the Hall-effect device as to cause the same to generate an output voltage proportional to the magnitude of the second fraction of the current flowing through the conductor, and hence to the magnitude of the complete current on the first current path terminal. Also included is an enclosure of electrically insulating material closely enveloping at least the first and the second conductor means.
The complete current detector is encapsulated in a preferred embodiment to be set forth subsequently, leaving exposed only parts of the current path terminals and other necessary terminals. The encapsulation conduces to reduction of a temperature difference between the first and the second conductor means to a minimum. The reduction of the temperature difference serves in turn to assure that the current is infallibly divided into the two fractions exactly at the predetermined ratio, such division being essential for accurate measurement of the current magnitude.
Another advantage of the encapsulation is the mechanical integration of the current paths and the Hall-effect device. The enhanced positional stability of these components is believed to diminish errors in current detection. Moreover, only partly projecting from the encapsulation, the current path terminals will be connected to an external circuit whose current is to be detected, in a manner that will not affect the accuracy of current detection or measurement.
The Hall-effect device may be conventionally formed in a semiconductor substrate having a main wording region where a voltage is generated in response to a magnetic field due to the flow of the second fraction of the current through the conductor of the second conductor means. Preferably, in this case, the conductor of the second conductor means may be formed in the shape of a substantially annular strip on the semiconductor substrate via an Insulating layer so as to encircle, as seen from above, the main working region of the Hall-effect device. The conductor can thus be situated as close as possible to the Hall-effect device and in a manner conductive to higher detection sensitivity.
The above and other objects, features and advantages of the invention and the manner of realizing them will become more apparent, and the invention itself will best be understood, from the following description taken together with the attached drawings showing the preferred embodiments of the invention.
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patent: 4123772 (1978-10-01), Janssen
patent: 5260614 (1993-11-01), Theus et al.
patent: 5426364 (1995-06-01), Yi
patent: 5604433 (1997-02-01), Theus et al.
patent: 5640085 (1997-06-01), Petr et al.
patent: 6232832 (2001-05-01), Kirkpatrick
patent: 53-7183 (1978-01-01), None
patent: 4-364472 (1992-12-01), None
patent: 10-282156 (1998-10-01), None
patent: 10-293141 (1998-11-01), None
Le N.
LeRoux Etienne P
Sanken Electric Co. Ltd.
Woodcock & Washburn LLP
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