Analysis of new SiC and GaN devices

In this paper, we analyze the static and dynamic behavior of some FET devices made of silicon carbide and gallium nitride. Companies are focusing on those types of components that allow the creation of high-efficiency converters and inverters. This article is a continuation of the previous one, which you can find here.

UnitedSiC‘with UJ4SC075006K4S SiC FET MOSFET and Transphorm‘s TP65H150G4PS GaN FET MOSFET for simulations

We will use some new generation SiC and GaN FET devices in the following tests and simulations that combine many of the advantages of newer technologies.

They can be summarized as follows:

• Excellent performance at high temperatures
• Low input capacity
• Low R_{DS (included)}
• Excellent recovery
• Presence of a diode for elimination of additional voltages
• ESD protection
• Special packages for fast switching and cleaner waves

The tested devices shown in Figure 1 are:

• UJ4SC075006K4S SiC FET MOSFET on UnitedSiC
• TP65H150G4PS GaN FET MOSFET on Transphorm

The first device UJ4SC075006K4S is very powerful, with included resistance (R_{DS (included)}) of only 6 mΩ and 750 V and is part of the SiC FET MOSFET family of nine parts of UnitedSiC. The component is based on the unique configuration of the cascode circuit. With R_{DS (included)} less than half that of the competition, the device has a short circuit endurance of 5 µs. The samples are available in TO-247-4L packages with four pins, and some in TO-247-3L packages with three pins. Cascade technology offers the advantages of broadband technologies, such as high speed, low operating losses at high temperatures, high stability and strength with integrated ESD protection. For application switching, the integrated diode is much faster than competing technologies. Its applications include propulsion and traction for electric vehicles, on-board and outboard chargers, unidirectional and bidirectional energy converters, renewable energy inverters and converters for all types. The second TP65H150G4PS device is a 650-V, 150-mΩ GaN sample and is a normally off component. It combines high-voltage GaN HEMT technology with low-voltage silicon MOSFET technology, offering highly reliable operation and excellent performance. The most important characteristics of the two power supplies can be seen in the table below.

Efficiency and R_{DS (included)} in static mode

The following simulation is used to evaluate and verify the efficiency values ​​of the power supply circuit in static mode, by checking the resistance of the drainage-source channel when the device is turned on. The diagram in Figure 2 shows the two devices being tested in the on state, the latter being provided with a direct voltage of 20 V at the gate. The system power supply is 500 V for 50 Ω load. The following table shows the measured data:

The calculation of R_{DS (included)} of both components is performed during the on state of the devices by performing the following equations:

The calculation of efficiency is also very simple and is used to estimate the amount of energy used profitably in the system and, in contrast, the losses in unused heat:

Efficiency and power losses in dynamic mode

Dynamic mode is most important, as this is where the components are tested. The systems are under great stress due to EMI, power losses, all associated inductive loads and switching of the components themselves. Figure 3 shows a general example of a PWM power supply, whose frequency in this case is about 500 kHz. The PWM signal is generated by two monolithic P- and N-channel MOSFETs. The reduction of some types of noise is carried out by ferritic grain, characterized by the following characteristics:

• Inductance: 0.38 µH
• Series resistance: 0.371 Ω
• Parallel resistance: 1600 Ω
• Parallel capacitance: 0.78 pF
• Impedance up to 100 Mhz: 266.5 Ω
• Max. impedance: 1,598.1 Ω
• Frequency of max. impedance: 292 MHz

Technology fights power outages (Figure 4). The imperfect nature of the components increases their dissipated power precisely at switching times.

The presence of the input and output capacity of the component, as well as its R_{DS (included)} and other elements contribute to power losses, which fortunately improve day by day.

The following is the efficiency achieved by the operation of both devices:

• Efficiency of SiC FET: 98.24%
• GaN FET efficiency: 99.02%

These are extremely high efficiencies, allowing almost all energy to be used actively, while maintaining low operating temperatures of the MOSFET.

In fact, B_ds the value in the on state is very low and the electronic switches hold almost perfectly.

The simulation can only be performed if the relative SPICE libraries of the two components used are available, can be downloaded from the Internet and include the following header:

.subckt UJ4SC075006K4S nd ng ns nss nss

and

.subckt TP65H150G4LSG 301 302 303

Conclusion

Designers should keep in mind that electronic simulations with power supplies can differ significantly from reality, especially if the systems contain inductive and capacitive components.

In addition, it must be remembered that power MOSFETs must always be powered by excellent drivers that provide high drive current at the gate, as capacitive input components prevent clear and immediate activation right at the gate.

Giovanni has always liked electronics, math and DIY. He is a computer programmer and teacher of computer science and mathematics. He loves shapes and is always looking for big prime numbers. He has also written a book on programming a PIC 16F84 microcontroller with mikroBasic. He is the owner of Electrosoft, a company that deals with electronics and information technology. He is a full-time coach and teacher.