GaN Transistor is First to Meet Short-Circuit Robustness Milestone for Motor Drive Applications

Transphorm has successfully demonstrated a five-microsecond short-circuit withstand time (SCWT) on a gallium nitride (GaN) power transistor.  

Transphorm GaN transistor reaches new SCWT milestone. Image used courtesy of Transphorm

 

The company claims the new short-circuit performance is the first-ever documented and serves as an important demonstration of the ability of GaN power devices to meet the robust standards of high-voltage power inverters in industrial motors, servo motors, and EV powertrains.   

To date, “heavy-duty” power applications have traditionally been served by insulated gate bipolar transistors (IGBT) and silicon carbide (SiC) technologies.  

The short-circuit performance demonstration was performed with strategic partner Yaskawa Electric Corporation, a global leader in low and medium-voltage drives, servo systems, and machine controllers.

 

Migrating GaN to More Robust Applications

For its power density, GaN remains a very attractive power conversion technology for higher voltage applications. GaN devices can generally operate at faster speeds, which translates to reduced switching losses, improved efficiency, and smaller, more power-dense form factors. These characteristics make GaN attractive for applications like servo systems and industrial robots that value power density.     

But to operate in higher reliability applications alongside IGBT and SIC solutions, GaN needs to demonstrate its robustness at higher power levels. Short-circuit survivability is one of the most challenging tests for high-voltage systems.   

Short-circuit conditions typically result in very high voltages and currents, well above rated,  that can be destructive to an end system. Detecting short-circuit conditions and initiating protective action can often take several microseconds. During this time, the power device, GaN or other, must withstand the high voltages and currents without permanent damage.

If the power semiconductor becomes damaged, the system becomes inoperable and must be taken out of service or repaired. This is not an acceptable option for mission-critical or high-reliability applications.   

Servo motor system. Image used courtesy of Yaskawa

 

Short-Circuit Testing

According to Transphorm, the new short-circuit capability was demonstrated on one of the company’s recently designed 5 mΩ, 650 V GaN devices.

Along with the short-circuit performance, the device supports a peak efficiency of 99.2% at power levels up to 12 kW during hard switching operations at 50 kHz.   

Transphorm will release additional details on the recent short-circuit testing, including a full description and demonstration analysis, at a major power electronics conference next year that is yet to be announced.    

 

Normally-Off Platform and Cascode Architecture

Umesh Mishra, Transform’s CTO and co-founder, highlighted the significance of the achievement, noting that standard GaN devices are only capable of short-circuit withstand times of a few hundredths of nanoseconds, falling well short of the microseconds required to safely detect and shut down during fault conditions.  

Mishra further said the key to Transphorm’s GaN short-circuit performance is cascode architecture and other aspects of their patented technology. 

For the company’s SuperGaN devices, a normally-off low voltage silicon MOSFET is cascoded with a normally-on GaN HEMT device to form a single transistor. The result is faster switching with superior reverse turn-off characteristics that make the devices well-suited to hard-switched bridge applications like motor drives and other power inverters.

SuperGaN switch design. Image used courtesy of Transphorm