Measuring Method Of Dynamic Loss Of GaN Power Transistor In Ultra-high Frequency Power Transistor Converter

Gallium nitride power transistors have attracted widespread attention because of their lower on-resistance than silicon devices and their application to higher switching frequencies.However,the dynamic loss of Ga N power transistors when switching at high voltage and ultra-high frequency is much higher than that at low voltage and low frequency.Charge trapping in Ga N power transistors causes dynamic on-resistance degradation,resulting in dynamic conduction losses that are much higher than theoretically calculated.The switching voltage charges and discharges the output capacitance of the Ga N power transistor to generate output capacitance loss,which is comparable in magnitude to the dynamic on-resistance loss.The classical method of measuring dynamic loss cannot be applied to the working condition of ultra-high frequency switching frequency.Dynamic losses will generate high dissipated power in the conductive channel and substrate,resulting in temperature rise that affects the operating characteristics of the power transistor and significantly limits the output power of Ga N applications.The dynamic on-resistance is closely related to the junction temperature of the power tube.The junction temperature is the temperature at the conduction channel and located inside the power tube,so the temperature sensor cannot measure the junction temperature.Aiming at the problem that it is difficult to measure the dynamic loss of Ga N power tubes under ultra-high frequency conditions,an indirect measurement method for the dynamic loss of Ga N power tubes is proposed.The no-load resonant switching circuit is designed,and the working waveform of the Ga N power tube is consistent with the working condition of the Ga N power tube in the UHF power converter.The drive control circuit was designed to realize zero-voltage switching,and the parallel connection of normally closed Ga N was used to realize the decoupling of output capacitance loss in the comparison experiment,and the dynamic on-resistance was calculated by using the indirect measurement method.Aiming at the problem that the internal junction temperature of the enhancement mode Ga N power tube cannot be directly measured,a transient electrical parameter method is proposed to measure the thermal resistance and predict the junction temperature.The simulation verifies the linear relationship between the source-drain voltage of the Ga N power transistor and the junction temperature,and verifies that the transient electrical parameter curve is fitted to the junction temperature cooling curve.Improve the Cauer thermal network model,and calculate the thermal resistance from the heating power.A thermal resistance measurement circuit is built to convert the transient electrical parameter curve into a junction temperature cooling curve,and the transient thermal impedance curve is calculated,and the thermal resistance from the conductive channel to the PCB is obtained by the transient double interface method.A three-dimensional finite element analysis is established for the dynamic loss measurement circuit to predict the junction temperature and the temperature distribution of the entire measurement circuit,and the thermal resistance of each level in the thermal network model is obtained.The dynamic loss measurement experiment adjusts different switching frequencies,driving voltages and peak voltages,and explores the influence of different working conditions on the dynamic on-resistance and output capacitance loss of two enhanced Ga N power transistors.It is found that the dynamic loss increases with the increase of switching frequency and peak voltage,while the driving voltage has little influence on the dynamic loss.The ambient temperature of the experiment was changed,and the junction temperature was predicted by the thermal network model.It was found that the higher the junction temperature,the greater the dynamic on-resistance of the Ga N power transistor,while the output capacitance loss was less affected by the junction temperature.