Protect power infrastructure and equipment
Power transmission and distribution systems, as well as sensitive equipment, require robust protection against damage from prolonged overloads and transient short circuits. With power systems and electric vehicles using increasingly higher voltages, the maximum potential fault current is also higher than ever before. To provide protection against these high-current faults, ultra-fast AC and DC circuit breakers are needed. Historically, mechanical circuit breakers have been the primary choice for such applications; however, solid-state circuit breakers are gaining popularity as operating requirements become more demanding. Compared to mechanical circuit breakers, solid-state circuit breakers offer several advantages:
Robustness and Reliability: Mechanical circuit breakers contain moving parts, making them relatively susceptible to damage. This means they are prone to failure or accidental automatic disconnection due to movement, and wear occurs with each reset during use. In contrast, solid-state circuit breakers contain no moving parts, making them more robust and reliable, less prone to accidental damage, and thus capable of undergoing thousands of open/close operations.
Temperature flexibility: The operating temperature of mechanical circuit breakers depends on their manufacturing materials, thus limiting their operating temperature. In contrast, solid-state circuit breakers operate at higher and adjustable temperatures, allowing them to adapt more flexibly to different working environments.
Remote configuration: Mechanical circuit breakers require manual reset after tripping, which can be very time-consuming and costly, especially when deployed on a large scale at multiple installation points, and may also pose safety hazards. Solid-state circuit breakers, on the other hand, can be remotely reset via wired or wireless connections.
Faster switching speed and no arcing: Mechanical circuit breakers can generate large arcs and voltage fluctuations during switching, enough to damage load equipment. Solid-state circuit breakers use a soft-start method to protect the circuit from these induced voltage spikes and capacitive inrush currents, and their switching speed is much faster, cutting off the circuit in just milliseconds in the event of a fault.
Flexible current ratings: Solid-state circuit breakers have programmable current ratings, while mechanical circuit breakers have fixed current ratings.
Smaller size and lighter weight: Solid-state circuit breakers are lighter and smaller than mechanical circuit breakers.
Limitations of existing solid-state circuit breakers
While solid-state circuit breakers offer several advantages over mechanical circuit breakers, they also have some drawbacks, including limited voltage/current ratings, higher conduction losses, and higher cost. Typically, for AC applications, solid-state circuit breakers are based on silicon controlled rectifiers (TRIACs), while for DC systems they are based on standard planar MOSFETs. The TRIAC or MOSFET handles the switching function, while an opto-isolated driver serves as the control element. However, for high-current applications with high output current, MOSFET-based high-current solid-state circuit breakers require heat sinks, meaning they cannot achieve the same power density levels as mechanical circuit breakers.
Similarly, solid-state circuit breakers implemented using insulated-gate bipolar transistors (IGBTs) also require heat sinks because the saturation voltage leads to excessive power loss when the current exceeds tens of amperes. For example, at a current of 500 amperes, a 2V voltage drop across the IGBT can result in a power loss of up to 1000W. For the same power level, a MOSFET would require an on-resistance of approximately 4 mΩ. As the voltage ratings of devices in electric vehicles move towards 800V (and even higher), no single device can currently achieve this level of resistance. While theoretically this could be achieved by paralleling multiple devices, doing so would significantly increase the size and cost of the solution, especially when bidirectional current needs to be handled.
Building Next-Generation Solid-State Circuit Breakers Using SiC Power Modules
Compared to silicon chips, SiC chips can be up to ten times smaller in size while maintaining the same rated voltage and on-resistance. Furthermore, SiC devices switch at least 100 times faster than silicon devices and can operate at peak temperatures up to twice as high. Simultaneously, SiC exhibits excellent thermal conductivity, resulting in better robustness at high current levels. ON Semiconductor leverages these characteristics of SiC to develop a series of EliteSiC power modules with on-resistances as low as 1.7mΩ for 1200V devices. These modules integrate two to six SiC MOSFETs in a single package.
Sintered-chip technology (sintering two separate chips into a single package) delivers reliable performance even at high power levels. Due to their fast switching behavior and high thermal conductivity, these devices can quickly and safely "trip" (disconnect the circuit) in the event of a fault, stopping current flow until normal operating conditions are restored. Such modules demonstrate the increasing possibility of integrating multiple SiC MOSFET devices into a single package to achieve low on-resistance and small size, meeting the needs of practical circuit breaker applications. Furthermore, ON Semiconductor offers EliteSiC MOSFETs and power modules with voltage withstand ranges from 650V to 1700V, enabling the creation of solid-state circuit breakers suitable for single-phase and three-phase residential, commercial, and industrial applications. ON Semiconductor's vertically integrated SiC supply chain provides near-zero-defect products that undergo comprehensive reliability testing to meet the needs of solid-state circuit breaker manufacturers.
Figure 1: ON Semiconductor's complete end-to-end silicon carbide (SiC) supply chain
The diagram below illustrates a modular implementation of a solid-state circuit breaker, where multiple 1200V SiC chips and switches are connected in parallel to achieve extremely low Rdson and optimized heat dissipation. These fully integrated modules feature optimized pin positions and layouts, helping to reduce parasitic effects, improve switching performance, and shorten fault response time. ON Semiconductor offers a diverse portfolio of SiC modules rated at 650V, 1200V, and 1700V, with some modules featuring a backplane and others without, to meet various application and efficiency requirements.
Figure 2: SiC B2B Module for Solid State Circuit Breakers - 480VAC -200A
Figure 3: ON Semiconductor modules suitable for solid-state circuit breaker applications
SiC technology and solid-state circuit breakers will develop together.
Mechanical circuit breakers offer lower power losses and higher power density, and are currently cheaper than solid-state circuit breakers. However, mechanical circuit breakers are prone to wear and tear from repeated use, and resetting or replacing them incurs expensive manual maintenance costs. With the increasing prevalence of electric vehicles, the market demand for circuit breakers and SiC devices will continue to grow, thus enhancing the cost competitiveness of this wide-bandgap technology and increasing its attractiveness to solid-state circuit breaker solutions. As SiC process technology continues to advance and the resistance of independent SiC MOSFETs further decreases, the power losses of solid-state circuit breakers will eventually reach levels comparable to mechanical circuit breakers, at which point power loss will no longer be an issue. Solid-state circuit breakers based on SiC devices offer advantages such as fast switching speeds, arc-free operation, and zero maintenance, resulting in significant cost savings and making them a widely adopted mainstream choice in the market.
