Five Things to Consider Before Switching to SiC in Power Conversion

2. Will it Impact the Rest of My Design?  

Here you have a choice. If you are upgrading an existing design that’s using IGBTs or Si-MOSFETs, just doing the swap and updating the gate driver as described will usually get the design up and running. This can give a useful system efficiency boost with the potential to reduce heatsinking, but there will probably be a net component cost increase. A ground-up new design would consider increasing switching frequency to gain further advantages, such as smaller passives and improved system dynamic response to load changes. However, these advantages are offset by a possible increase in dynamic losses at the higher switching rate. 

3. Do I Really Need High-Frequency Switching?  

A headline characteristic of SiC is its potential to switch at high frequency. However, the corresponding increase in switching losses in ‘hard-switched’ conversion topologies may be unworkable, forcing a change to ‘soft-switched’ or resonant arrangements. These are generally more complex and can have limitations, such as trading lower dynamic for higher static losses for a given power transfer. A good reason to increase switching frequency is to reduce the size and cost of magnetics. However, in some applications such as motor drives, the magnetic element is the motor itself, which is sized for the power it delivers, so this advantage is not present. For this reason, many motor drives still operate around 10kHz and here, the low conduction losses, high voltage capability, ruggedness and low cost of IGBTs are still attractive. If a frequency ‘sweet spot’ is found where a SiC device has total lower dynamic and conduction losses than an IGBT in a motor drive, in an industrial environment for example, the energy saved may still be minor compared with the value for the load. The motor driver can be smaller though, which is a benefit. However, with advancements in SiC technology from suppliers like Nexperia, designers now have access to MOSFETs that balance conduction and switching losses to deliver a compelling alternative.

4. How Will it Impact My Passives? 

To get the most benefit, any efficiency increase achieved can be leveraged by reducing power converter heatsinking size, weight and cost while maintaining safe junction temperatures. Alternatively, for the same heatsinking and die size, junction temperatures are lower and reliability higher. In practice, SiC die sizes are smaller than IGBTS for the same headline ratings so junction temperatures can actually be higher, and although SiC as a material can stand much higher temperatures than Si, the limit is practically set by device packaging. By utilizing SiC, it might be possible to eliminate heatsinking completely, or cooling air dramatically reduced. If an increased switching frequency is considered, magnetics can be reduced in size, with weight and cost savings. Usually, capacitor values can be reduced at higher switching frequencies, such as in input and output filtering, for further economies. In some cases, the reduced capacitor values allow higher-performance ceramic types rather than electrolytics with their limited lifetime.