Measurement of the common source inductance of typical switching device packages

The common source inductance is one of the major causes of deterioration of the switching speed and susceptibility of the false triggering for semiconductor switching devices. Practical design of this inductance requires selection of an appropriate semiconductor package because this inductance is greatly dependent on the physical package structure. However, few studies have reported a list of the common source inductance of commercially available packages. In order to list and compare the common source inductance among typical semiconductor packages, this paper carried out measurement of this inductance of actual switching devices mounted on experimental PCBs. This paper employed a recently proposed straightforward measurement technique directly applicable to switching devices mounted on PCBs. As a result, a basic database of the common source inductance of typical packages was presented. The common source inductance was found to be determined mainly by the package type. However, in TO-247 and TO-220 packages, approximately one-third of the total common source inductance was found to possibly vary among the switching devices of the same package due to the dependence on the current rating. Investigation of the physical package structure implied that this dependence was caused by the stray inductance of the bonding wires connecting the semiconductor chip to the source terminal.