Circulating Current in Conductor Line of Open-Circuit after Semiconductor Device Turn-Off

For example, a semiconductor element is turned off in a power supply circuit. A part of the circuit becomes an open-circuit. The magnetic energy stored by the parasitic inductance of the conductor line in the open-circuit is then released as circulating currents flowing within the conductor line. The circulating current flows symmetrically between the left and right sides of the conductor line, which is divided into two parts widthwise. The author clarified this circulating current by measuring the local magnetic field on the conductor line using the optical probe type magnetic field sensor. In addition, this paper describes in detail the current density distribution and the magnetic field of the circulating current in conductor lines of various cross-sectional shapes. The analysis results revealed that the integrated current density within the conductor line is zero regardless of the cross-sectional shape of the conductor line, but circulating currents flow. Also the magnetic field around a highly symmetric cylindrical conductor line is zero. On the other hand, the magnetic field increases as the aspect ratio increases, as in the case of a less symmetrical rectangular conductor line.