Custom modules built with SiC MOSFETs minimize the impacts of short circuits and overloads
Nearly every electrical engineer has wondered at some point whether it is possible to design a non-mechanical circuit breaker. There are plenty of reasons for this line of thought: would it not be better to use semiconductors to interrupt faults or handle overload conditions?
However, deeper investigation inevitably reveals major obstacles. For one thing, the breakdown voltage of familiar power devices is around 600 V. Consequently, even for low-voltage industrial applications below 480 V, many of these devices must be connected in series to form viable circuit breakers.
Another challenge is heat generation. When current flows through any semiconductor device, power loss produces substantial heat due to significantly higher on-resistance compared with traditional metal contacts. Since this heat must be dissipated, the entire architecture of conventional circuit breakers needs to be reconsidered from the ground up before developing a solid-state alternative.
Given all these technical hurdles, why pursue solid-state circuit breakers at all? After all, mechanical devices have reliably served circuit protection needs for more than a century.
Combating Arc Flash Hazards
Unfortunately, mechanical circuit breakers are far from ideal when it comes to mitigating arc flash—the destructive energy released during short-circuit events. When a mechanical breaker attempts to cut off fault current, a delay of 8 ms or longer is typical. While 8 ms is extremely fast for a mechanical response and essentially represents the physical limit of contact separation, it is an eternity from an electrical perspective.
During these critical milliseconds, short-circuit fault current can surge as high as 10 kA to 100 kA, depending on the rating of the upstream transformer. The energy dissipated at the fault location is proportional to the square of the current and accumulates over time. In such fault conditions, energy releases so rapidly that it triggers arc explosions accompanied by molten metal. Only afterward does the mechanical breaker dissipate massive internal arc energy to clear the high-magnitude fault current.
A mitigating factor is that power grids operate with alternating current rather than direct current. This means fault current naturally crosses zero at some point within each half-cycle, helping extinguish arcs inside mechanical breakers.
Over the past two decades, industry efforts have focused on educating engineers about arc flash risks. Nevertheless, the root cause has not been resolved, as the mechanical speed of contact opening cannot be improved. Current practices only aim to minimize arc flash damage: reinforcing switchgear enclosures, training technicians on proper personal protective equipment for breaker operation and live-line work, and adopting current-limiting circuit breakers and fuses to suppress short-circuit current magnitudes.
None of these approaches deliver a fundamental solution. The ideal remedy is to isolate faults within microseconds or less, eliminating arc flash risks entirely. With the commercial realization of solid-state circuit breakers, a revolution in electrical infrastructure is on the horizon.
Challenges in Selective Coordination
Electrical protection design relies heavily on selective coordination: any fault within a distribution system must be cleared by the nearest downstream breaker, without causing widespread power outage across the entire system.
Mechanical circuit breakers have wide tolerance bands in their time-current characteristics. As a result, upstream breakers must be intentionally set with longer time delays than downstream units to maintain coordination.
A practical example illustrates this tradeoff. Consider an industrial system fed by a 2000 A main breaker, which supplies a 150 A downstream breaker for a chiller system. The 150 A mechanical breaker has a clearing time ranging from an optimal 8 ms to a worst-case 13 ms. To avoid full-system shutdown during a chiller short circuit, the upstream 2000 A breaker must be rated for a minimum clearing time longer than 13 ms. In practice, this forces the upstream breaker to operate with an average delay of 20 ms or more, further exacerbating arc flash exposure.
In stark contrast, solid-state circuit breakers are free from mechanical clearing time limitations. They deliver ultra-fast fault response at the point of failure, drastically reducing the overall response time required for coordinated circuit protection.
The SiC Solution
Advancements in other industries have accelerated the development of solid-state circuit breakers. Over the past decade, the electric vehicle market has driven demand for high-voltage, high-efficiency power converters. These innovations have boosted vehicle energy efficiency and extended driving range. The core enabler is next-generation power devices featuring ultra-low on-resistance and minimal power loss. Operating at higher voltage levels reduces current magnitude for equivalent power ratings, cutting consumption of copper and other conductive materials while lowering overall weight and system cost.
Major manufacturers have invested heavily in silicon carbide (SiC) device development. Today’s SiC MOSFETs, IGBTs and JFETs offer blocking voltages up to 1700 V with far lower on-resistance than conventional silicon counterparts. SiC power devices also feature vastly faster switching speeds, enabling smaller inverters with lower switching losses and potentially lower system costs. These advancements make SiC devices ideal candidates for low-voltage circuit protection applications.
Off-the-shelf 900 V to 1200 V SiC MOSFETs are now commercially available, delivering much lower on-resistance than silicon chips of equivalent die area. For low-voltage circuit protection systems rated up to 1000 V, these high-blocking-voltage SiC devices are perfectly suited for deployment.
Most commercially available SiC components are designed for inverter applications, supporting DC-DC, AC-DC and DC-AC power conversion. Their standard packaging is not optimized for solid-state circuit protection, often resulting in overly large form factors if repurposed directly. An additional complication is that MOSFETs must be configured in a common-source topology to support bidirectional voltage blocking for AC operation. For these reasons, solid-state circuit breakers require fully customized power modules.
On-resistance is a critical design parameter for SiC MOSFET-based breakers, typically ranging from 10 mΩ to 20 mΩ—far superior to silicon devices, which often exceed 60 mΩ with lower voltage withstand capability. Even with SiC technology, on-resistance remains a significant consideration for high-current operation. For instance, a single 10 mΩ SiC MOSFET carrying 100 A dissipates 100 W of power. Two such devices connected in series for breaker operation dissipate a total of 200 W, requiring dedicated heat sink infrastructure for thermal management.
A key advantage of SiC MOSFETs is natural current sharing when operated in parallel. Since resistance increases with temperature, higher current flow through one device raises its junction temperature and on-resistance, diverting current to parallel devices until thermal and electrical equilibrium is achieved.
When multiple SiC MOSFET dies are placed closely on the same substrate, their thermal coupling is tightly matched. A symmetrical layout ensures balanced current sharing and equivalent stray inductance, capacitance and inherent resistance across all parallel current paths. With this architecture, designers can parallelize devices as needed to reduce overall on-resistance to any target value. The practical limits are ultimately determined by cost constraints and the required form factor of the solid-state breaker.
Module Design Considerations
Designing power modules for solid-state circuit protection differs fundamentally from designing inverter modules. Inverter modules prioritize high-speed switching with minimized parasitic inductance and capacitance to reduce switching losses. Circuit protection devices, by contrast, spend nearly their entire service life in a continuous on-state, with only rare on-off switching events throughout their operational lifespan.
For protection module design, it is imperative to maintain matched inductance and capacitance across all parallel devices. This balance becomes critical during overload or short-circuit events, when current surges rapidly and gate voltage is pulled low to turn off n-channel devices. Uniform current decay across all parallel units prevents uneven electrical stress. Additionally, all gate connections to parallel devices must feature identical impedance to ensure consistent turn-off characteristics. Adhering to these design principles ensures equal stress distribution across all dies during fault interruption, maximizing module durability and reliability.
Package design must also minimize total on-resistance by optimizing metal traces on the substrate and wire bonding layouts, while maximizing thermal cooling for each SiC die to lower internal junction and module operating temperatures.
Founded in 2014 and headquartered in Charlotte, North Carolina, startup Atom Power has developed a custom 900 V, 250 A power module following these rigorous design guidelines. The module achieves a total on-resistance of 7 mΩ, with turn-on and turn-off switching times of just 0.1 μs. This proprietary module serves as the core of the company’s Atom Switch solid-state circuit breaker—the first device of its kind to earn certification from Underwriters Laboratories (UL), the independent authority on safety standards.
Certified to UL 489, the integrated Atom Switch incorporates current sensing, intelligent monitoring and control functions within optimized packaging. It virtually eliminates arc flash risks and drastically reduces tripping time. The product has been validated under extreme short-circuit conditions up to 100 kA, 150 kA and even 200 kA.
Atom Switch is engineered for seamless integration into custom panel enclosures, ensuring proper mounting, communication interfaces and efficient heat dissipation to maintain optimal module cooling.
Typical short-circuit interruption delay for the Atom Switch is 40 μs—far longer than its intrinsic 0.1 μs switching speed. The additional latency stems from fault current rise time, fault detection processing and control signal propagation. Even so, 40 μs is approximately 200 times faster than the quickest mechanical breakers available today. This ultra-fast interruption reduces let-through fault energy by up to 4,000 times.
Another key benefit of SiC-based breakers is extended service life. Unlike mechanical breakers, they do not require replacement after clearing multiple full-rated short-circuit faults. For mild overload conditions (1 to 2 times rated current), tripping characteristics can be programmed with exceptional precision, achieving timing accuracy better than 1%. By comparison, mechanical breakers typically have a timing tolerance of up to 10%.
The next-generation Atom Switch platform will integrate ground-fault and arc-fault circuit interruption capabilities. Enabled by advanced algorithm-based control logic, these upgrades will resolve nuisance tripping issues commonly associated with mechanical breakers—especially the inherent limitations of traditional devices in detecting and mitigating arc faults.
Beyond Traditional Circuit Protection
Solid-state circuit breakers offer transformative advantages far beyond basic overcurrent and short-circuit protection. Their time-current characteristics can be fully adjusted via software, enabling a single hardware platform to serve multiple application scenarios and adapt dynamically to changing operating environments after installation.
Additional built-in capabilities include self-monitoring and predictive diagnostics. Integrated intelligence enables solid-state breakers to perform real-time self-diagnosis, verify operational integrity, and issue early warnings of potential faults before catastrophic failures occur. Mechanical breakers lack this capability; latent defects are typically only discovered after a fault event, often resulting in costly downtime and equipment damage.
Native remote controllability makes solid-state breakers ideal for demand-side energy management and microgrid islanding operations, supporting seamless integration of backup power and distributed generation systems. They can also function as soft starters for induction motors and transformers, eliminating inrush current spikes and extending equipment service life.
At present, the upfront cost of solid-state breakers remains higher than conventional mechanical alternatives. However, their superior safety performance, enhanced functionality and long-term operational benefits far outweigh initial price differences. Their adoption often eliminates the need for additional auxiliary equipment and resolves critical safety vulnerabilities, delivering compelling total cost of ownership advantages.
Driven by rising SiC production to meet demand from electric vehicles, smart grids and solid-state circuit protection markets, component costs are projected to decline steadily. While mechanical circuit breakers will not disappear overnight, their decades-long dominance in circuit protection is clearly coming to an end.
