Identification of Power BJT Operating Stages Based on Experimental Excess Charge Estimation

The paper proposes and demonstrates an experimental way of estimating the amount of stored charge of excess minority carriers within power BJT base and collector. This consequently allows a detailed identification of transistor operating stage.A brief device operation analysis is provided as a clear support of the measured characteristics.The method is based on determining the steady-state stored charge at various operating conditions by integration of negative transient base current during turn-off event which deflates the stored charge.An ultimate objective of these and future experiments is an accurate interpretation and modelling of various device stages during IGBT switching process. Most of the observed phenomenons are common among a power BJT and IGBT’s intrinsic BJT. As IGBT doesn’t provide access to the internal base current, it is advantageous to measure and interpret the relations between stored charge and switching waveforms of power BJT first and further generalize the observations to IGBT measurements.