Reduced size, weight, and power (SWaP) and increased standardization requirements for applications from unmanned aircraft to ground vehicles to portable communications systems are driving military power supply designs. Meanwhile, innovations such as gallium nitride (GaN) and silicon carbide (SiC) are improving efficiencies.

Mission priorities drive requirements for military applications, and that is no different for power supplies. For example, to enable persistent surveillance, sensor payloads need more efficient power and the push toward more portable electronics for warfighters requires the same efficiency but in smaller and smaller footprints – pressuring power supply designers to innovate more than ever before.

“Power supplies are in demand across multiple segments such as avionics, unmanned aerial vehicles (UAVs), payloads, vetronics, mission computing, to name a few,” says Tom Curatolo, Director, Global Defense & Industrial Business Development, Vicor (Andover, Massachusetts). “Persistent surveillance is a common requirement for UAV intelligence, surveillance, and reconnaissance (ISR) payloads that can translate to longer-duration missions. This often means their power supplies need to have higher efficiency to reduce the energy dissipated as heat and thus maximize the UAV’s mission endurance.

“Often, due to the airframe’s construction, the space allotted is either equal to or less than what they had before when they had less of a power demand,” Curatolo continues. “The payloads deployed on UAVs put the emphasis on size and weight of the overall system, which typically translates to redesigning the power supply. This drives the major challenge: selecting the right technology for the power system.”

Smaller footprints

Demand for reduced SWaP-C (SWaP plus cost) in power supplies is nothing new. “Everyone still wants power supplies to be smaller, lighter, more efficient, and at a lower cost, SWaP-C-optimized,” says John Santini, Vice President of Power Engineering, at Data Device Corp. (DDC – Bohemia, New York).

For example, “In military vehicles, users are looking for higher power because they’re doing more and more from the vehicle,” Santini continues. “We’re also seeing significant activity in portable electronics. There are a lot of portable applications where you see a greater demand for higher power density. Today, soldiers are carrying more electronics than ever before. Powering all the electronics requires batteries and highly efficient power conversion to maximize the available power from this limited source of energy.”

The power supply tech is getting smaller, faster, and more efficient. “Everything is driving towards meeting requirements under SWaP-C,” says Robert Russell, Vice President, Product Marketing at Vicor. “UAVs are a great example of lowering SWaP and cost; as UAVs become more and more prevalent, new power topologies, technologies, and architectures need to mature in some of these markets to satisfy the needs of the user.”

Reduced SWaP in power supplies is also consistent requirement in military UAV platforms. UAVs are a major factor in the next phase of power distribution in critical systems because “UAVs and other military systems are requiring much more power, and this is forcing people to rethink busing current around at 28 volts,” Russell adds. “System architects will need to move up to 48 volt, 380 volt, or even an 800 volt-plus bus for certain applications like tethered UAVs.” (Figure 1.)

Figure 1: Vicor’s DCM is an isolated, regulated DC-DC converter. With its high-frequency zero-voltage switching (ZVS) topology, the DCM converter delivers high efficiency across the input line range. Photo courtesy of Vicor.

Managing the heat

Thermal management in power supplies is another important factor to consider.

Adding electronics to an existing platform is a challenge for designers who see no end to the demands for “higher-power, higher-efficiency power supplies,” says Lou Garofolo, Product Manager – Power Supplies & Instruments, at North Atlantic Industries (NAI – Bohemia, New York). In particular, he says, “The military market strictly looks for conduction-cooled, rugged power supplies. In addition, BIT [built-in test], monitoring, and communication features are required in most power-supply applications (Figure 2).

Figure 2: The VPX57-31 offers continuous background built-in test (BIT), high-efficiency, and current-share capabilities. Photo courtesy of North Atlantic Industries (NAI).

“NAI is seeing a trend toward VPX conduction-cooled power supplies, in both 3U and 6U form factors; we are seeing great success with our VPX product line,” he adds.

VPX thus becomes an option due to its high-power capabilities. Companies including Milpower Source are “actively designing and shipping new higher-power 3U VPX VITA 62 power supplies for customers requiring tailored solutions, which not only deliver increased power density, now above 1 kW, but also offer integrated features such as hold-up and embedded MIL-STD-461 EMI filters,” says Tomer Eshed, General Manager at Milpower Source (Belmont, New Hampshire) (Figure 3). “Our design and manufacturing process, utilizing discrete components, allows us to reduce integration risk and future obsolescence.”

Figure 3: Milpower Source’s 3U VPX power supply. Photo courtesy of Milpower Source.

Pushing densities and efficiencies: GaN and SiC

While reduced SWaP drives many requirements for power supplies, innovation is happening with gallium nitride (GaN), a particularly hot technology within military applications such as radar and electronic warfare and silicon carbide (SiC).

“New technologies such as silicon carbide MOSFETS have been trending in recent years, enabling higher power densities and operational temperatures for military subsystems,” Eshed notes. “Similarly, GaN is becoming more prevalent to continue this trend.

“Battery chemistries offering higher power capacity at smaller physical volumes are an additional area we are exploring here at Milpower Source,” he adds. “We are anticipating leveraging battery technologies specifically to soon offer advanced uninterruptible power supply (UPS) solutions for the naval environment.”

Santini concurs. “Today, if you’re looking for game-changers, some of the new semiconductors, SiC and GaN, have shown us a path to raise switching frequencies and reduce losses, especially silicon carbide in higher power applications,” Santini adds. “For instance, for shipboard 440-volt AC systems, SiC is a game-changer for lowering losses and enabling higher switching frequencies.

“Within a power supply, once you raise the switching frequency, everything just starts to shrink, so that’s a way to take it to the next level in terms of being more compact,” Santini continues. “Although similar to SiC, GaN tends to be a lower-voltage switching device and performs best in low-voltage applications. It’s another technology which is enabling higher switching frequencies, and consequently helping to shrink power supplies and increase their efficiency.”

Driving standards and commonality

Another trend driving the future of power supply designs is the DoD’s desire for more commonality and standardization in its electronic systems. “Two key items which will be very important and possibly game changers are first, requirements to fully comply with VITA 46.11 and second, environmental requirements that if your products are stated to comply with the environmental of VITA 47, you must have a complete data package to present to customers,” Garofolo says.

“VPX VITA 62 power supplies are a standardized form factor that will reduce the life cycle costs of many military platforms, supporting an open architecture approach to DOD platform integration,” Eshed says. “The ability to customize the pinouts, filtering, and holdup features of a VITA 62-compliant power supply is a game changer for the defense industry.”

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