Page 29 - NEW Armstrong Book - 2

positive forward current. The reverse-recovery time (trr) thus becomes an important index to define the characteristics of a MOSFET. Figure 2 shows a comparison between the trr of a 1,000-V Si-based MOSFET and a SiC-based MOSFET. As can be seen, the body diode of the SiC MOSFET is extremely fast: The values of trr and reverse-recovery current (Irr) are so small as to be negligible, and the energy loss (Err) is consider- ably reduced.
SiC design
While three-level and other Si circuit topologies are emerg- ing to improve efficiency, new SiC designs are arriving that meet growing high-power requirements for electric vehi- cles. SiC will strengthen the power grid and reduce losses.
Tobias Keller, vice president of product marketing at Hitachi ABB Power Grids, highlighted his experience in the SiC field. “Silicon carbide already started on voltage levels of 750 V and 1.2 kV,” he said. “Depending on conduction and switching losses, SiC will find its way to traction in the industry on volt- age levels of 1.7 and 3.3 kV.”
Jan Huijink, technical marketing manager at WeEn Semiconductors, noted that the main components of an industrial or server power supply “are the PFC and the LLC full-bridge, [where] the benefit of using SiC components is that faster switching speeds can be achieved.” As a result, he said, “passive components can be smaller, making the whole application smaller, lighter, and lower-cost. In an unin- terruptible power supply, the SiC components that we find are diodes and MOSFETs. They mostly find their way into the input circuitry, like rectification and PFC, and in the inverter.”
SiC devices have benchmark switching performance of much higher frequency and virtually no reverse recovery. This superior and stable switching performance is independent of temperature. SiC’s ability to withstand higher operating volt- age, current, and switching frequency, together with high efficiency and excellent thermal management, makes this semiconductor the ideal replacement for silicon in several power applications, including automotive. Used in EV trac- tion inverters, SiC is confirmed to support longer range and more efficient drive-cycle performance.
Maurizio Di Paolo Emilio
is editor-in-chief of Power Electronics News and EEWeb.
Semiconductors based on SiC offer higher thermal conductivity, higher electron mobility, and lower power losses. SiC diodes and transistors can also operate at higher frequencies and temperatures without compromising reliability.
15
Technology Analysis The Next Wave of Semiconductors with SiC