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Desaturation Detection for Paralleled GaN Phase Legs

Image of FUL desaturation detection with load.
Fig. 1. FUL desaturation detection with load.
This paper discusses short circuit protection for paralleled gallium-nitride (GaN) phase legs. Desaturation detection is chosen for implementation in paralleled GaN phase legs, due to its design structure and effectiveness. A gate driver integrated circuit (IC) from STMicroelectronics featuring the desaturation detection function is chosen to drive paralleled GaN high electron mobility transistor (e-HEMT) phase legs. Finally, short circuit protection results under both hard-switching fault (HSF) and fault under load (FUL) cases are discussed.

The phase leg is shorted under 400 V dc bus voltage, with the inductive load connected to the top switches. Fig. 1 shows the results under FUL and HSF in the desaturation detection scheme with inductive load. Fig. 2 shows the same group of short circuit test results, but with no load connected to the phase leg. The test results illustrate that when the phase leg is shorted, the short circuit current can reach up to 500 A. When the voltage across drain and source exceeds 3 V, the GaN e-HEMT is turned off after a 150 ns delay. For the case of FUL, the bottom switch is turned off when the voltage on bottom gate driver desaturation-sensing pin first reaches the threshold voltage. For HSF, the top switch is turned off.

This paper discusses the desaturation detection for paralleled GaN phase leg under FUL and HSF conditions. With desaturation detection, the paralleled e-HEMT GaN phase leg successfully passed the shortcircuit test. In future work, the degradation effect of each shorcircuit on GaN e-HEMT will be studied to further justify the reliability of the protection scheme.

Image of HSF desaturation detection with load.
Fig. 2. HSF desaturation detection with load.
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