The advantages of GaN technology in different applications
Meeting the growing demand for high energy efficiency and high power performance while continuously reducing costs and size is the main challenge faced by the power electronics industry today.
The introduction of the relatively new wide bandgap compound semiconductor material gallium nitride (GaN) indicates that the power electronics industry is moving in this direction. Moreover, as the commercialization of this technology continues to increase, its application market is growing rapidly.
The quality factor (FOM), on-resistance RDS(on), and total gate charge (QG) of the high electron mobility transistor (HEMT) gallium nitride (GaN) are all superior to those of the corresponding silicon-based devices. At the same time, it has a very high drain-source voltage withstand capacity, zero reverse recovery charge, and very low parasitic capacitance.
Power conversion of electrical energy is the first field to widely apply GaN technology, which can meet more stringent energy efficiency requirements, making GaN the preferred solution for improving energy efficiency in power conversion systems. The higher switching frequency of GaN enables the power conversion system to achieve higher power density, miniaturization and lightweighting, and reduce costs.
In motor control design, both size and energy efficiency are of great significance. Minimizing the conduction and switching losses of the driver is the key to energy conservation and consumption reduction.
As the power density, breakdown voltage and switching frequency of silicon-based transistor technology approach their theoretical limits, it is becoming increasingly difficult to enhance the performance of motor drives by relying on traditional silicon-based MOSFETs and IGBTs. In high-voltage motor control applications, GaN transistors with superior electrical characteristics have become an effective alternative to MOSFETs and IGBTs.

Promote the development of the next-generation motor inverters
GaN is even expected to bring significant advantages to the application of low-frequency switches (up to 20kHz). In the field of household appliances, motor drive systems such as washing machines, refrigerators, air conditioners, and vacuum cleaners mainly rely on inverters to control motor speed, torque, and energy efficiency. Due to mechanical and functional limitations, the actual size of household appliance motors is basically fixed and unchanging, which is different from industrial servo motors or precision motors. This means that the traditional method of reducing the overall system size by downsizing the motor itself is not feasible - instead, the inverter that drives the motor and the corresponding power electronic devices must be improved.
In this sense, it should be pointed out that compared with traditional silicon-based transistors, GaN products are not particularly outstanding in a single parameter, but have a significant overall performance advantage in all aspects.
The reverse recovery charge (Qrr) of GaN is very small and can actually be ignored, and its parasitic capacitance is very low. Therefore, it can withstand a slightly higher voltage change rate dV/dt. Although the motor windings and insulation limit the maximum allowable value of dV/dt, the ability of GaN to operate at higher switching speeds enables designers to meticulously optimize the switching edges.
In addition, GaN switches can safely and significantly reduce the dead time without the risk of direct bridge arm transmission. The conversion time between the upper and lower bridge arm switches can be easily shortened to one-tenth of that of silicon-based transistors. A shorter dead time can improve the energy efficiency of inverters, reduce switching losses, and at the same time, it will not affect the reliability of the motor.
Despite such a significant performance improvement, it is far from over. In fact, all these "small" improvements, when added together, ultimately lead to what might be the most crucial point among all the improvements: saving on radiators.


Say goodbye to the radiator
The significant reduction in dissipated power enables designers to slim down the bulky heat sinks in the inverter power conversion stage, or even abandon them. Nowadays, assembly lines may require fewer manufacturing processes. The absence of a radiator also means there is no need for screws or installation joints, thus avoiding mechanical failures that may occur after long-term use of the equipment, which is expected to save maintenance costs.
The overall result is that the inverter design has become smaller and lighter, with better economic benefits and is more suitable for the demanding and highly competitive home appliance market.

The waveform shown in Figure 2 indicates that the temperature rise of GaN in the relevant tests is very low and smooth. In the above example, the typical RDS(on) of the device under test is 80mΩ. The switching frequency of the motor inverter is 16 kHz, and the maximum value of dV/dt is slightly lower than 10V/ns.
This GaN switch tube can safely output approximately 800 W of power without thermal runaway. The temperature rise Δt is less than 70 °C, and there is sufficient safety margin before reaching the maximum operating junction temperature (TJmax) of 150 °C.
This excellent test result was achieved without installing a heat sink. The GaN is installed on a general-purpose two-layer PCB and dissipates heat through the circuit board itself.

STPOWER GaN transistor
The STPOWER GaN transistor is essentially a normally off p-GaN gate enhancement mode transistor with zero reverse recovery charge. There are currently a total of seven products of STPOWER GaN 700 V rated breakdown voltage (VDS) transistors. The typical on-resistance RDS(on) range is from 270 mΩ TO 53 mΩ, and they are packaged in DPAK, PowerFLAT 8x8 and TO-LL.
This product portfolio is expanding rapidly, adding products with different packages, RDS(on), and breakdown voltages.

Author：

Ester Spitale, Technical Marketing Manager of stmicroelectronics
Albert Boscarato, Manager of stmicroelectronics' Application Laboratory

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