Power Electronics Europe Issue 4 - November 2022

www.wolfspeed.com WBG DATACENTER 29 www.power-mag.com Issue 4 2022 Power Electronics Europe based CCM totem pole PFC can have not only higher efficiency but higher power density at similar or lower cost. A comparison of efficiency between technologies clearly shows that while both SiC- and GaN-based CCM totem pole PFCs can achieve >99 % efficiency, GaN has the efficiency advantage only at very light loads. As discussed earlier, GaN’s much higher R DS(ON) change over temperature (Figure 2) results in its dramatically drooping efficiency curve at higher power/loads. In applications, like datacenters, that operate at or near full load 24/7, GaN therefore fails to meet efficiency requirements. SiC, on the other hand, provides an efficiency similar to that of GaN at half load and better efficiency at full load (Figure 6). Taking a broader look to include power density, the number of components, and relative cost of SiC- and GaN-based CCM totem pole PFC (Table 2), it is noted that SiC is better than GaN not only in terms of efficiency in high-power density applications, but also in terms of gate drive complexity, control, and cost. In yet another comparison of real-word WBG demonstrator designs from various companies, Wolfspeed SiC shows clear advantages (Table 3). Some key points to note are: Many of the existing reference designs require impractical thermal management and restrict design flexibility. GaN FET-based totem-pole designs have lower efficiency at full load due to the high temperature coefficient of R DS(ON) . As expected, SiC’s low temperature coefficient of R DS(ON) results Wolfspeed’s design to exhibit a nearly flat efficiency curve from half load to full load. While SiC and GaN meet requirements for bridgeless PFCs in the 2-4 kW range, high conduction losses make GaN thermal design challenging beyond 4 kW. System frequencies of the reference designs are limited to the 45-47 kHz and Figure 6: Silicon Carbide is the best choice in a totem pole PFC, especially for high reliability applications Table 2: Topology and component analysis of Silicon Carbide- and GaN-based bridgeless PFCs Table 3: A competitive analysis of wide bandgap reference designs on the market