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How Silicon Carbide devices boost ampacity in power circuits?

Dr. Daniel Martin
Jan 11, 2021
Chinese (中文)
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Ampacity, the current-carrying capacity of a power device, is usually one of the biggest factors limiting the performance of a power design. It is crucial for a design engineer to have a component which performs well under the given thermal management requirements of the design.

Power devices can deliver output current according to the switching frequency, device loss mechanisms, and thermal management from die junction to cooling medium. Ampacity-related ratings of components serve as guidelines for selecting parts. Depending on the design and component specifications, the options available out of the wide range of products on the market is narrowed down to just a select few. That provides power system designers a finite set of products to simulate and select the closest amperage device to meet the system requirements while optimizing performance and system bill of materials (BOM).

Wide bandgap (WBG) semiconductor devices offer relatively high ampacity as compared to traditional silicon. They can significantly improve power density in high power designs, and are becoming a preferred choice for designers of such circuits. These devices are exceptional in delivering high ampacity because of their low conduction and switching losses. Silicon Carbide (SiC), a widely accepted WBG semiconductor material, perfectly meets the designer’s requirements by handling higher power in a smaller space with greater efficiency. Find how Silicon Carbide components perform in your design by using our SpeedFit Simulator.

The Wolfspeed WolfPACK TM is an all-SiC device that facilitates the integration of circuit topologies in a single package to achieve high ampacity for power circuit demands in a standard footprint. The modules are compact in size, simple to implement, and can perform better in some system designs than multiple discrete devices to form the same configuration. This is due to the consolidating of connections and packaging on a single substrate, thus eliminating the need for further isolation insertion or additional parasitics. You can learn more about Wolfspeed WolfPACK, its performance, and other specifications, on the Wolfspeed WolfPACK family page.

Figure 1: Wolfspeed’s latest power module offering, the Wolfspeed WolfPACK, offers industry leading Silicon Carbide in a well-known, rugged industrial package for ease of implementation.
Figure 1: Wolfspeed’s latest power module offering, the Wolfspeed WolfPACK, offers industry leading Silicon Carbide in a well-known, rugged industrial package for ease of implementation.

Let’s now look at some of the conditions such as temperature, switching frequency, and heat dissipation, and how they impact overall ampacity and power system performance.

Temperature

A module’s rated DC amperage is based on the package’s thermal resistance, system’s thermal management implementation, and electrical resistance (Rdson) in the package at the maximum rated junction temperature. As the power device’s temperature increases, the device delivers lower output currents due to its temperature relationship with Rdson. Silicon Carbide power devices have lower on-state losses and no built-in potential voltage drop (as in legacy components in this footprint on the market today), yielding a best-in-class performance for Wolfspeed WolfPACK modules.

Switching Frequency

Switching frequency, or the number of times a device is turned on and off per second, often leads to an increase in dynamic losses and reduction in average output current carrying capability. Increasing the switching frequency of a system is generally highly desirable, as it allows for smaller passive devices—capacitors, filters, inductors, etc.—to be used. Silicon Carbide devices featuring low dynamic losses allow circuit designers to push the maximum available switching frequency, while still at high bus voltages, boasting considerably higher power density ratings than their silicon counterparts.

Heat Dissipation

One main factor that significantly affects ampacity per device is heat dissipation. As noted, Silicon Carbide devices produce fewer losses, and through implementation on a single ceramic substrate, the need for additional voltage isolation to heatsink can be avoided. This minimizes the thermal resistance to the cooling ambient, thereby affording designers simpler system implementation, with minimal thermal management costs and real estate.

Figure 2: The graph highlights how Wolfspeed WolfPACK modules implement complex topologies with only two bolts, secure press fit pins to PCBs, and provide ceramic isolation to the coldplate.

Ampacity

The factors described above altogether determine a module’s output ampacity. Given that Silicon Carbide power devices have lower Rdson and lower dynamic losses, the resulting RMS output current in switching applications increases over legacy semiconductor technology. Additionally, coupling in the isolated package minimizes thermal resistance, so the amperes of available current in the footprint are again increased. This fact, coupled with the high-speed controlled switching of Silicon Carbide devices in Wolfspeed power modules, allows for the highest value of usable RMS amps per SiC area delivered to the load. This increase in capability per module can be used in the form of more RMS current, minimized junction temperature, and/or increased system efficiency.

Conclusion

As can be seen, high ampacity can play a significant role in ensuring the power performance of modules targeted at mid-range power applications, including but not limited to EV charging, railway traction, industrial automation, motor control, industrial power supplies, and renewable energy designs (such as solar inverters). This is because it enables flexible and scalable modules that can serve power designs ranging from single kilowatt to hundreds of kilowatts.

A holistic approach to maximizing ampacity, offered by power modules like the Wolfspeed WolfPACK, helps reduce cost, minimize design complexity, and improve overall system performance. Moreover, it simplifies the prototyping and manufacturing of power products.

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CAB006M12GM3
GM3
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1200 V
200 A
6 mΩ
Gen 3 MOS
150 °C
62.8 mm x 56.7 mm
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1200 V
200 A
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150 °C
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GM3
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1200 V
194 A
8 mΩ
Gen 3 MOS
150 °C
62.8 mm x 56.7 mm
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1200 V
146 A
8 mΩ
Gen 3 MOS
150 °C
62.8 mm x 56.7 mm
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FM3
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105 A
11 mΩ
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150 °C
62.8 mm x 33.8 mm
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1200 V
78 A
16 mΩ
Gen 3 MOS
150 °C
Yes
FM3
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1200 V
51 A
21 mΩ
Gen 3 MOS
150 °C
62.8 mm x 33.8 mm
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1200 V
40 A
32 mΩ
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150 °C
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