Non-destructive evaluation of the circuit-dependent turn-off limits of gate turn-off thyristors by the detection of the local current density

This paper presents an improved analytical tool for the characterization of local power dissipation during turn-on and turn-off. The applied measurement system combines two previously published methods resulting in a new technique for the detection of the spatial current density distribution during the switching processes. The first method yields the radial detection of the current density by a set of concentric Rogowski coils integrated in the cathode pole piece. The second method measures the radial and tangential components of the magnetic field along the circumference of the GTOs. To evaluate the sensitivity and the spatial and time resolution of this method, different samples with lateral and radial inhomogeneities of the carrier lifetime have been prepared. The detected distributions of the current density are compared with the electrical and technological data in different GTO segments