Twenty years ago, choosing a transistor for an application was relatively straightforward, especially since options were almost exclusively silicon-based. Today, engineers are given the luxury (and perhaps the burden) of having a plethora of different transistors at their disposal—whether they be conventional silicon, SiC, GaN, or others.
A comparison of different semiconductor options available. Image used courtesy of Messina et al‘s “first and euRopEAn siC eigTh Inches pilOt line” (REACTION) project via ResearchGate. [accessed 26 Mar, 2021]
With all of these options, a process as fundamental as component selection can slow down a design cycle. Once an engineer chooses the type of transistor to use, then he or she must choose from a number of different brands and materials.
Now, UnitedSiC has released a calculator tool that allows engineers to more easily pick a FET for their designs without simulating or bench testing through a number of options.
A New SiC Tool
UnitedSiC is hoping to streamline the selection process with a new tool called the FET-Jet Calculator.
This calculator is a free online tool that helps designers select a device by comparing the performance of SiC FETs for different applications and topologies as well as environmental and electrical parameters.
Screenshot of the FET-Jet calculator. Image used courtesy of UnitedSiC
UnitedSiC asserts that the calculator helps predict system performance without some of the tedious hands-on testing processes. Some of the metrics calculated include:
- Overall efficiency
- Component losses (dynamic and conduction contributions)
- Junction temperatures
- Current stress levels
The tool will also issue a warning if a resulting voltage is higher than the rating of a given part.
How It Works: FET-Jet Features
After trying the calculator, it seems to be a very useful tool with an array of features.
The tool is an application-based component finder, where right off the bat, you’re asked to choose what application you’re looking to create—either AC/DC, DC/DC, or DC/DC isolated. Once your application is chosen, you’re prompted to select what specific topology you’re using. For example, within AC/DC applications, you can select between PFC, TPPFC, Vienna, and two-level voltage source inverter topologies.
Input parameters and device selection for a boost converter from the FET-Jet calculator. Image courtesy of UnitedSiC
You can then select your desired input parameters, including power rating, switching frequency, heatsink temperature, as well as topology-specific parameters.
The calculator will then output values for peak currents, losses per FET, losses per diode, total losses, and efficiency. Then, with all of this information calculated, it will offer you UnitedSiC FETs and diodes for your application, given the input parameters and topology you entered.
One consideration, however, before using this calculator for SiC FET, is whether the component you want to use should be SiC or silicon.
Silicon vs. SiC
In many ways, SiC blows silicon out of the water concerning performance.
SiC is considered a wide-bandgap semiconductor with a bandgap that can reach up to 3.3eV instead of ~1.2eV for silicon. On top of this, SiC exhibits higher hole and electron mobility values than Si. As a result of these two characteristics, SiC can withstand much higher voltages, with a breakdown voltage of 600 V, and exhibit higher efficiency due to faster switching speeds and lower RDS(on).
Representation of power loss for Si and SiC. Image used courtesy of Mitsubishi Electric
With so many seemingly superior options on the market, one might question why you would ever use conventional silicon transistors.
The real strength of silicon is that it has been around the longest. The result of this is that the industry has made silicon products very accessible and affordable. If your application can afford a lower-performing transistor, then silicon may be the best bet for the sake of cost and mitigating concerns about component availability.
UnitedSiC is not the only company offering tools for FET selection. EPC offers a tool for filtering GaN FETs, ROHM has a similar tool for MOSFET selection specifically for synchronous rectification DC/DC converters, and TI has a FET loss calculator for synchronous buck converter applications.
Being able to quickly and accurately choose your application’s suitable component is crucial to a successful design. How do you typically compare FETs during the design process? Do you utilize tools like this one? Share your methods in the comments below.