Prospect Analysis of SiC and GaN for Power Conversion

I believe many of you have heard of semiconductors, then you know that silicon carbide (SiC) and gallium nitride (GaN) semiconductors have advantages over silicon semiconductors in power applications (especially in the power supply market). However, designers working with these broadband semiconductors (wide bandgap) face real-life challenges.

Although silicon semiconductors will remain mainstream for many years, in certain applications customers can take advantage of the properties of wide-bandgap semiconductors, including improved bandgap (eV), breakdown field (MV/cm), thermal conductivity (W/ cm-K), electron mobility (cm2/Vs) and electron drift velocity (107 cm/s). Without getting into the details of semiconductor physics, it can be said that these improved parameters make wide-bandgap semiconductors suitable for high-voltage, high-switching-frequency applications while improving power density and heat dissipation.

Customers demand smaller, lower temperature, and more efficient products. Power supplies are a dynamic market, and wide bandgap technology enables designers to achieve these improved design goals. The main advantages of wide bandgap semiconductor power switches include high current density, faster switching speed and lower drain-source on-resistance (RDS(on)). From the end customer's perspective, these device performance improvements can deliver significant system-level benefits. In real-life applications, customers can achieve high-temperature operation and reduce overall system size and weight. But designers need to understand that designing with wide bandgap technology requires some additional work during the design phase.

While traditional silicon semiconductors are limited to switching frequencies of a few hundred kilohertz, both SiC and GaN can extend into the megahertz range (Figure 1). Increased switching frequency allows the use of smaller magnetic components in designs, but also introduces electromagnetic interference (EMI) challenges. This is just one example of where designers need to be cautious.

Smaller, cooler, more efficient

Increasing switching frequency is one of the best tools available to designers. While the advantages of increasing switching frequency, such as lower losses and reduced size, are highly desirable, there are risks. Faster switching speeds result in higher switching transients. For example, in the latest power converter designs based on GaN power switches, switching times are approximately 10 to 20 times faster than traditional systems. Faster switching speeds (5 ns typical) and high voltage rails (≥600V) result in increased transient voltages (≥120kV/µs); therefore, the common-mode transient immunity (CMTI) of isolated gate drivers plays a key role.

Industry standard junction isolation and optocoupled gate driver CMTI values ​​for signal integrity and latch-up immunity are below required levels. Capacitively coupled and transformer coupled gate drivers greatly improve performance. The latest capacitive coupling solutions specify CMTI for signal integrity up to 200 kV/µs and latch-up immunity up to 400 kV/µs, making them best suited for the high-frequency systems being designed today.

real world applications

Let’s consider the advantages of SiC and GaN in some practical applications. Off-board charging of electric vehicles (EVs) is one of the most interesting and fastest-growing applications, including the market for fast chargers and charging stations. SiC can really add value in this application.

Engineers may be designing fast-charging products for various customer groups, such as municipalities, businesses, and EV owners, and each product has slightly different design goals. This is not an exhaustive list, but some of the most important goals are reliability, small size, lightness, and efficiency while keeping charging times to 30 minutes or less. SiC devices can help achieve all of these goals.

In addition to the power stages mentioned above, designers must select the appropriate devices for gate drive. Proper SiC gate drivers need to support fast switching times of high-power MOSFETs and high system efficiency, and they need to be robust in inherently noisy environments.

In practice, this means that gate drivers must drive high currents and must have low latency and high noise immunity. Careful system-level design will result in a charging station that is reliable, performs well, and is compact. One might think that designers adopting breakthrough technologies would need to compromise on cost, but the reality is that leveraging the advantages of SiC will reduce the overall cost of the charging station.

As for the expansion of GaN into real-world applications, wireless charging is one of the hottest areas. As wireless charging becomes an increasingly common trend in mobile phones, GaN enables industrial customers to take advantage of the technology as well. At high frequencies, GaN shows the most obvious advantages over silicon. Silicon is used in lower power applications, but as application requirements scale to tens of watts and even kilowatts, efficiency becomes increasingly important. Customers can benefit from higher switching frequencies, which not only improve efficiency but also provide other advantages. The above is an analysis of the prospects of SiC and GaN for power conversion. I hope it can be helpful to everyone.