Switching Experimental And Signal Analysis Of Power MOSFET Under Low Voltage Based-on Acoustic Emission Technology

Generally,voltage,current and other electrical parameters are adopted as the detection indicators to test power MOSFET reliability in traditional methods.In recent years,the emerging detection methods advance rapidly include chip junction temperature detecting,thermal impedance detecting,and giant magnetoresistance fields detecting.For the effective monitoring for the power MOSFETs health status,it is necessary to meet the requirements of reliability,fast,and non-intrusiveness.The detection and monitoring methods based on acoustic emission（AE）technology can meet its requirements,which could reflect the health status of the power MOSFET under working conditions in future.A new direction for improving the reliability of power MOSFETs is carried out by the emerging detection and monitoring methods.The AE technology to research the state of power MOSFETs has been adopted in this thesis in first time,so the preliminary generation of AE phenomena and the signal propagation process are analyzed in low-voltage switch tests condition.By analyzing the signals process,the mechanism is verified at the same time.First,according to the package structure of the discrete power MOSFET device,the procedure from the generation to capture by AE sensor is shown in the micrograph.After the missions accomplished,the switching circuit are designed.The test circuit board used in the power MOSFET switching process and the multi-channel AE signal detection system are introduced.The broken lead test is utilized to check the completing construction of the hardware system as well.Next,the AE signals from broken lead test are compared with the electromagnetic-AE signals by figures and parameter tables.Then two modern methods are adopted to process AE signal.After that,the connections established between time domain,frequency domain parameters to power MOSFET electrical parameters finally.It can be found that the electromagnetic-AE signal is composed of elastic waves and electromagnetic waves.Through time-domain and frequency-domain signal analysis,the conclusion can be draw that there is a strong linear relationship between the peak value of the turn-on pulse when the drain current signal appears and the drain-source voltage V_ds in the time-domain.It can clearly observe the moment when high-frequency electromagnetic waves are generated due to the drain current by the short-time Fourier time-frequency diagram.At the same time,it can be found that the main range of high-frequency components is probably 2MHz to 3MHz.A strong linear relationship between the amplitude of the time-domain signal with the gate-source voltage V_gs can be shown up in the elastic wave parts.At the same time,the peak value of the 155k Hz frequency band of the frequency-domain waveform can be utilized to establish a linear relationship with the gate-source voltage V_gs.The drain-source voltage V_ds affects slightly the amplitude-frequency characteristic curve in all range.The Hilbert transform is used to draw the envelope of the low-pass processed signal,and it is found that the acoustic emission signal under the same gate-source voltage V_gs has almost the same waveform envelope.And using the variational modal decomposition algorithm,when the optimal modal number K is met,it is found that there is an almost identical modal component under the same gate-source voltage.Finally,through the test under nearly rated voltage,the electromagnetic-AE signal detected by the damaged power MOSFET during the test,which has been compared with the signal in the healthy status.It is found that multiple peaks appeared in low-frequency waveform,and inconsistent with the healthy state waveform.From the frequency-domain,it can be found that the high-frequency part is nearly not exist,which is quite different from the high-frequency component in the healthy status.The application prospects primarily have been proved by exhibiting AE signal to monitor the status of power MOSFETs.The thesis establishes the relationships between the electrical parameters of the power MOSFET and the characteristic parameters of the electromagnetic-AE signal by exploring the electromagnetic-AE signal captured by the power MOSFET under the switching test mode.The comparison is used between the AE signal generated by the power MOSFET in healthy and damaged status in the experiment.Technical guidance is provided preliminary for the utilization of AE technology to detect and monitor the status of power MOSFETs,and a new direction for evaluating the reliability of power electronics is also concluded.