As an disclosure related to a conventional transformer, a common-mode noise filter described in, for example, Japanese Patent Laid-Open Publication No. 2006-24772 is known. FIG. 10 is a configuration diagram of the common-mode noise filter 500 described in Japanese Patent Laid-Open Publication No. 2006-24772.
The common-mode noise filter 500 includes a first coil 510, a second coil 520, lead-out portions 511, 512, 521, and 522, and external electrodes 513, 514, 523, and 524. The first coil 510 and the second coil 520 have the same spiral shape. The second coil 520, when viewed in a plan view, is positioned so as to deviate slightly from the first coil 510.
The external electrode 513 is provided on the left side surface. The external electrode 523 is provided below the external electrode 513 on the left side surface. The external electrode 514 is provided on the right side surface. The external electrode 524 is provided below the external electrode 514 on the right side surface. The lead-out portion 511 connects the first coil 510 and the external electrode 513. The lead-out portion 512 connects the first coil 510 and the external electrode 514. The lead-out portion 521 connects the second coil 520 and the external electrode 523. The lead-out portion 522 connects the second coil 520 and the external electrode 524.
In the common-mode noise filter 500, the first coil 510 and the second coil 520 have the same shape, and therefore have the same length. As a result, the first coil 510 and the second coil 520 can be approximated in terms of their inductance values.
However, the common-mode noise filter 500 has an issue in that it is liable to cause a difference between the first coil 510 and the second coil 520 in an inductance value. More specifically, the lead-out portion 511 is led out toward the upper left. Accordingly, a current it flowing through the lead-out portion 511 is directed in the opposite direction to a current i2 flowing near the lead-out portion 511 within the first coil 510. As a result, the magnetic field that is generated near the lead-out portion 511 within the first coil 510 is directed in the opposite direction to the magnetic field that is generated by the lead-out portion 511. Therefore, the inductance value of the first coil 510 decreases.
On the other hand, the lead-out portion 521 is led out toward the lower left. Accordingly, a current i3 flowing through the lead-out portion 521 is directed in the same direction as a current i4 flowing near the lead-out portion 521 within the second coil 520. As a result, the magnetic field that is generated near the lead-out portion 521 within the second coil 520 is directed in the same direction as the magnetic field that is generated by the lead-out portion 521. Therefore, the inductance value of the second coil 520 increases. Thus, the common-mode noise filter 500 is liable to cause a difference between the first coil 510 and the second coil 520 in an inductance value.