Military Embedded Systems

Mil system power is cheaper by the dozen (volts)


May 02, 2013

Eran Strod


Today open standard VME and VPX boards come in three flavors of power: 3.3 V, 5 V, and 12 V. As a result, system designers have to daily confront the extra work and cost of designing custom power supplies when the different boards they select for their...

Today open standard VME and VPX boards come in three flavors of power: 3.3 V, 5 V, and 12 V. As a result, system designers have to daily confront the extra work and cost of designing custom power supplies when the different boards they select for their system design fall into some mix of the three voltage types. The problem resurfaces when it’s time to upgrade the system, since an entirely new power supply with a different mix of voltage types might be required to support the technology refresh. However, there’s a better way to solve this challenge – one that delivers some very real, easy-to-understand SWaP-C benefits.

50,000-foot view: Why homogenous 12 V works best

In recent years, some of the leading COTS vendors have standardized on 12 V as the single power type for all of their new Intel, Power Architecture, FPGA, and GPGPU-based VME and VPX modules. Eliminating the aforementioned mixed-voltage “Tower of Babel” will result in simpler, cleaner, and more easily scaled system designs. One fundamental advantage of standardizing on 12 V is that it is ideal for use in military platforms. 12 V is evenly divisible into the common 48 V telecommunications power supply de facto standard, which makes it easy to take advantage of the wide range of choices and cost efficiencies that flow out of the commercial telco market.

12 V also works natively with the most popular off-the-shelf AC/DC conversion modules found on military platforms. Reducing platform-to-backplane conversion increases power efficiency. Eliminating conversion saves power that would otherwise be wasted. Even better, it reduces space and weight in the system since a single standard 12 V backplane supply can be used to support all boards in the system. Eliminating the need to convert the platform vehicle power source into separate DC power of 12 V, 3.3 V, and 5 V signals on the backplane enables the system designer to achieve greater efficiency and space savings in the chassis subsystem.

System-level view: Pure 12 V benefits

These days, every system designer is tasked with simplifying their designs and supply chains to lower the overall hardware cost of ownership. The single 12 V approach eliminates the time, cost, and hassle of sourcing, maintaining, and storing multiple different power supplies or developing custom chassis supplies. And once a single voltage becomes the standard, it eases, speeds, and simplifies the development of system variants. In one real-world example, a 17-slot system designed to support 12 V boards requires three power slots for three distinct power supplies. If the design included a mix of 12 V and 3.5 V boards, two additional slots out of the 17 available would have to be dedicated to 3.5 V power supplies. Thus, the decision to standardize on 12 V comes from having a system-level view.

Let’s say an SBC was based upon 5 V and a DSP module was based on 3.3 V power. The number of boards would drive the requirement for different amounts of each supply. This would mean a specific power supply for each configuration of boards. A configuration that used two SBCs and one DSP board might need a different power supply than a configuration that used one SBC and two DSP boards. This drives up cost, increases complexity, and reduces the ability to adapt a platform architecture to multiple applications. Not so when all the boards standardize around 12 V. With commonality around 12 V, a single supply can accommodate many different mixes of boards.

Additionally, a 12 V HPEC system could leverage a single system design and leverage that box into many easily configurable variants to address many different applications. An example is the Curtiss-Wright HPEC platform, which offers Intel SBCs, PowerPC SBCs, DSP boards, GPGPU boards, FPGA boards, and VPX switches that can be mixed and matched to meet different application requirements. All of these boards operate principally off of 12 V so the integrator doesn’t get into a trap of choosing a power supply with a certain amount of 3.3 V, 5 V, and 12 V power.

Thwarting the mixed-voltage power dilemma

It’s easy to remember: Power comes cheaper by the dozen volts. A homogenous 12 V plan frees the design from custom power supplies, saves slots, simplifies logistics, cuts system weight, and provides opportunities to leverage standard commercial telco power supplies. And because integrators are increasingly trying to leverage intellectual property from one program to others, in today’s cost-conscious world, it might just be a matter of survival to operate 12 V lean and mean.

Eran Strod System Architect Curtiss-Wright Controls Defense Solutions


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