Bench Talk

(Source: Littelfuse)

As a mountain bike enthusiast, I take calculated risks. For me to improve, I must push myself to jump over obstacles more quickly, increase my speed, and cut corners tighter while at the same time conserving energy for a strong finish. Though adventurous, I am far from being a daredevil attempting and succeeding in landing fantastic canyon jumps (Figure 1) like the skilled mountain bike riders in the Red Bull Rampage YouTube videos. At each stage of the race, my goal is to close the gap between my actual performance and my potential.

Figure 1: Cyclist jumping on a bicycle between two giant boulders. (Source: anatoliy_gleb - stock.adobe.com)

Like mountain biking, industrial applications are always better with increased efficiencies and power. One of the ways this gap is being jumped is by employing Wide Bandgap technology. Wide Bandgap technology is constantly improving, and more offerings are becoming available and more affordable than just a few years ago. This blog will discuss how Littelfuse Silicon Carbide (SiC) products are ideal for applications where improvements in efficiency, reliability, and thermal management are desired.

All Littelfuse SiC MOSFETs are optimized for high-frequency, high-efficiency applications (Figure 2). These SiC MOSFETs offer low gate charge, low output capacitance, and low gate resistance for high-frequency switching. These devices also feature low drain-source on-state resistance. These MOSFETs’ low gate charge and on-resistance translate into lower conduction and switching losses. Littelfuse offers in-house designed, developed, and manufactured SiC MOSFETs with low gate charge and output capacitance, industry-leading performance, and ruggedness at all temperatures. Littelfuse SiC MOSFETs come in a variety of packages, configurations, and voltage and current classes. Typical industrial applications that can benefit from using SiC-MOSFETs include motor drives, photovoltaic (PV) solar inverters, Uninterruptible Power Supply (UPS) systems, and modular multilevel converters.

Figure 2: Applications that benefit from SiC-MOSFETs due to increased efficiency include motor drives, PV solar inverters, UPS systems, and modular multilevel converters. (Source: romaset - stock.adobe.com)

Let’s look more closely at one specific example. It is a use case related to the low-cost design and high performance of a 60W auxiliary switched-mode power supply (SMPS). Using a 1700V-class device, such as SiC MOSFETs from Littelfuse, specifically their LSIC1MO170E0750 N-Channel SiC MOSFET offering (Figure 3), allowed the power supply to accept a wide range of input voltages from 300V to 1kV.

Figure 3: LSIC1MO170E0750 N-Channel SiC MOSFET offers low gate charge resistance and ultra-low on-resistance for high-frequency switching applications. (Source: Mouser Electronics)

A simple low complexity design with high reliability is required to ensure that the auxiliary supply does not become a limiting factor to system reliability. Single-switch flyback topology is the most common selection for low-power DC-DC power conversion due to its simple structure, lowest component count, and low cost. However, there are several challenges to selecting silicon MOSFETs for a single switch flyback topology for auxiliary power supply applications. In a flyback topology, the power switching device must have the voltage capability to withstand a total system voltage that addresses the highest input supply, transformer induced effects, secondary reflected voltage, and circuit arrangement/layout effects.

At 1000V input, the peak voltage on a power switching device can be easily over 1200V, making it challenging to select silicon (Si) MOSFETs with proper blocking voltages. A 1500V Si MOSFET will have a low margin and raise reliability concerns. Si MOSFETs rated 2000V and above can provide a sufficient margin. Still, the specific on-state resistance is much higher than lower voltage MOSFETs, reducing converter efficiency and compromising heat management. This consequence may necessitate more extensive cooling solutions even for a low power conversion application. In addition, the cost of >2000V rated Si MOSFETs is much higher. Two-switch flyback or other topologies should be employed to use Si MOSFETs rated 1500V and lower. However, the design complexity and converter component counts will increase significantly in a two-switch flyback topology.

Solution: 1700V_DS, 750mΩ SiC MOSFET

The introduction of 1700V SiC MOSFETs provides a possible solution by using a simple single-switch flyback topology for such applications to achieve a wide input voltage range. The 1700V breakdown voltage provides enough voltage margin even for 1000V input voltage. The specific on-resistance of a 1700V SiC MOSFETs is much lower than that of a 2000V-device and above rated Si MOSFETs.

Additionally, SiC MOSFETs have lower switching losses compared to Si MOSFETs. Lower switching losses also provide an option to increase the switching frequency of the auxiliary power supply to reduce transformer size and weight.

The TO-247 package it comes in also provides a large surface area and good thermal conductivity for simpler thermal management than smaller outline packages for low voltage devices.

WBG for Industrial Power Supply Solutions

With Littelfuse's Wide Bandgap SiC MOSFETs, designers can narrow the gap with a greater margin to achieve their power-supply and efficiency solutions. One thing is for certain. It is much easier to close this gap than to jump my bike across my next chasm.

Paul Golata joined Mouser Electronics in 2011. As a Senior Technology Specialist, Paul contributes to Mouser’s success through driving strategic leadership, tactical execution, and the overall product-line and marketing directions for advanced technology-related products. He provides design engineers with the latest information and trends in electrical engineering by delivering unique and valuable technical content that facilitates and enhances Mouser Electronics as the preferred distributor of choice.

Before joining Mouser Electronics, Paul served in various manufacturing, marketing, and sales-related roles for Hughes Aircraft Company, Melles Griot, Piper Jaffray, Balzers Optics, JDSU, and Arrow Electronics. He holds a BSEET from the DeVry Institute of Technology (Chicago, IL); an MBA from Pepperdine University (Malibu, CA); an MDiv w/BL from Southwestern Baptist Theological Seminary (Fort Worth, TX); and a PhD from Southwestern Baptist Theological Seminary (Fort Worth, TX).