1. Field of the Invention
The present invention relates to a current sensor that detects a current flowing in a to-be-measured current path, and more particularly to a current sensor that detects a current flowing in a to-be-measured current path by using magneto-electric conversion elements.
2. Description of the Related Art
To control or monitor an electronic device, a well-known current sensor is attached to a to-be-measured current path to detect a current flowing in the current path. As this type of current sensor, a current sensor that uses magneto-electric conversion elements such as Hall elements or magneto-resistive elements is known. It is known that a plurality of elements are used to improve the sensitivity of the magneto-electric conversion elements and reduce adverse effects by external magnetic fields.
A current sensor 900, which is an proposed conventional current sensor, has a concave cut into which a to-be-measured current path (not illustrated) is interposed, as illustrated in FIG. 17 (see Japanese Unexamined Patent Application Publication No. 2001-066327). FIG. 17 is a perspective view that schematically illustrates the structure of the current sensor 900 described in Japanese Unexamined Patent Application Publication No. 2001-066327. The current sensor 900 in FIG. 17 has a case 920 that has a concave cut 911 in which a to-be-measured current path is interposed, a circuit board 910 having a cut 921, the circuit board 910 being placed in the case 920, and magneto-electric conversion elements (here, Hall elements) 930 and 931 that output electronic signals according to the intensity of a magnetic filed generated by a current flowing in a conductor placed in the vicinity of the concave cut 911. Thus, the current sensor 900 that can be made compact and easy-to-integrate can be provided.
Another known current sensor has four magnetic impedance elements that are oppositely placed, centered around an electric wire holder, which holds an electric wire (see EP1037056 A1). This current sensor has an arc-shaped opening, which works as the electric wire holder, at an engagement portion of a case having a convex part and a concave part. On the concave part side of the case, the four magnetic impedance elements are oppositely placed around the opening in its circumferential direction so as to be equally spaced.
To achieve higher measurement precision than in the above conventional technologies described in Japanese Unexamined Patent Application Publication No. 2001-066327 and EP1037056 A1, current sensors having more magneto-electric conversion elements can be contemplated. FIGS. 13A and 13B are plan views of current sensors in comparative examples. FIG. 13A illustrates a current sensor according to a first comparative example, in which eight magneto-electric conversion elements C15 are positioned at positions at which they surround a to-be-measured current path CB. FIG. 13B illustrates a current sensor according to a second comparative example, in which six magneto-electric conversion elements C25 are positioned at positions at which they surround the to-be-measured current path CB. To simplify an explanation, only the to-be-measured current path CB, neighboring current paths CN, and the magneto-electric conversion elements C15 and C25 are illustrated.
As illustrated in FIGS. 13A and 13B, the current sensors in the comparative examples each have a plurality of magneto-electric conversion elements (C15 or C25) positioned on a circumference centered on the center of the to-be-measured current path CB in a plan view; each two adjacent magneto-electric conversion elements (C15 or C25) are spaced at the same angular interval. Specifically, the magneto-electric conversion elements C15 of the current sensor in the first comparative example in FIG. 13A are placed at the vertexes of a regular octagon. The magneto-electric conversion elements C25 of the current sensor in the second comparative example in FIG. 13B are placed at the vertexes of a regular hexagon. Thus, even if the position of the to-be-measured current path CB is shifted a little, when detected values from the magneto-electric conversion elements (C15 and C25) are added, it is possible to prevent measurement precision from being easily lowered.