Plasma extraction transit time（PETT） oscillations are a type of self-excited oscillations found in high-voltage bipolar devices and of important potential application value in the state monitoring of power semiconductor modules. Consequently

we investigated the oscillation waveform parameters that are significantly coupled to turn-off currents and analyzed the physical mechanism. A PETT oscillation test platform for high-voltage press-pack IGBT chips was designed and fabricated

and PETT oscillations between two IGBT chips were detected under different turn-off currents. The relationship between the turn-off current and a series of typical oscillation waveform parameters was presented. To explain the experimental rules

we proposed a new equivalent circuit of PETT oscillations and an intuitive graphical analysis method. From the experimental results

it is found that there are apparent monotonic coupling relationships between the turn-off current and the start time

peak time or end time of oscillations with the growth rate of about 0.1 μs/A

which can be adequately explained by the graphical analysis method. Furthermore

it is deduced that there is a linear relationship between the logarithmic value of the turn-off current and the start time

peak time or end time of oscillations

and the inference is confirmed by the experimental results.