Size & Cost-Optimized Power Solutions for Non-tethered Applications

In the world of electronics, power solutions (i.e., power supplies, power conversion devices, energy storage, safety components, and related interconnects/boards/cables, etc.) are commonly perceived as an inconvenient necessity. Obviously, nothing runs without power, but conversely, most designers and engineers would rather focus on optimizing their systems for the application and the overhead to keep the system running.

As luck would have it, there is the additional annoyance of power solutions quite often driving the majority of system size/weight, bill-of-materials (BOM) costs, and even bottlenecking the overall, system development schedule. One can always drill deeper into headaches associated with power solutions (such as those related to supply chain and manufacturing), but that is neither the focus nor the goal of this white paper. As a matter of fact, it is our hope that the contents of this document and the additional resources referenced may help to actually reverse these negative perceptions of yesteryear and bring one optimistically into a more sustainable future.

Some of the most common figures of merit (FOM) for a system are its size, weight, and power (a.k.a., SWaP factors) characteristics. When combined with a cost metric, this can also be referred to as SWaP-C factors. Given the point above about power solutions being famous for dominating these FOMs in the overall system design, it naturally makes sense that these characteristics are under a microscope, specifically regarding the system components that make up and/or are closely related to the power subsystem. Power density is typically a function of the total available power versus overall solution volume, and it is the reason why component size tends to have an inverse relationship with power density. The power density metric is taken a step further when combined with overall solution mass (typically translated to weight on Earth), which can be a critical FOM in non-tethered applications, as is reviewed from many perspectives in the content that follows.

In terms of the components comprising power solutions, the primary ones driving SWaP (and sometimes –C) factors are the filter components in the form of magnetics (i.e., transformers, inductors, toroids, chokes, etc.) and capacitors (i.e., bulk/electrolytic caps, safety caps, etc.). These often enable compliance with safety and other standards, such as those for critical requirements of electromagnetic compatibility (EMC) and protection against dangerous voltage and/or energy surge levels, in addition to power conditioning. Given how significant filter components can be to driving SWaP factors in undesired directions for what may outwardly appear to be “benign circuits” to the core application, it cannot hurt to regularly remind oneself as to why they exist and why the motivations for meeting such requirements go beyond clearing off some regulatory checklist item.

It should also be noted that while filter components can look fairly rudimentary from a circuit schematic/diagram perspective, the construction and implementation of such devices can be deceptively complex, particularly when it comes to both meeting compliance targets and optimizing SWaP-C factors.

This is where it can behighly beneficial to utilize commercial products for filtering and protection , which are designed by experienced professionals.

Even though commonly disaggregated throughout a system, components related to interconnects (i.e., wires, cable assemblies, connectors, etc.) can contribute significantly to SWaP-related challenges, especially in transportation modalities. A modern vehicle can easily contain over a mile’s worth of wiring and therefore, also contribute considerably to the overall weight. This is only trending up and to the right of the curve in the rush to electrify drive trains and bring sensor-based intelligence, advanced computing, and wireless communications to mobility applications.

While the application space of electronics can be a very wide spectrum, thermal mitigation techniques can be quite significant contributors to a system’s size and weight. Heatsinks can become very bulky, particularly in passively-cooled or conductively-cooled use cases. In forced-air solutions, fans may not only occupy a significant amount of overall system volume but may also require a non-negligible amount of power themselves, thus compounding the overall, SWaP-related challenges. This should also serve as a reminder for the perpetual quest for improving power supply efficiency, which translates to the reduction of dissipated power and facilitating the mitigation of nearly every design challenge stated here related to SWaP-C factors and beyond [1].

Some applications may have extensive requirements for packaging that can offer be more significant contributions to size and weight, such as an enclosure/chassis and even potting material [2] used to encapsulate the electronics. System requirements driving these SWaP contributors can range from reliability, such as in the case of environmental protections from external factors such as temperature, humidity, dust, conductive particles (a.k.a., foreign airborne metallics), and even hermetic sealing for waterproofing and/or safety reasons. Non-engineering motivations can also come into play here, such as the need for security from prying eyes and reverse engineering.

So far, all the components and solutions described here have been in the context of SWaP factors, but just about any system or application will have a sharp focus on cost and lead to a SWaP-C analysis. It would be irresponsible to dictate highly-generalized rules of thumb in terms of component versus cost tradeoffs because of the wide spectrum of solutions for each component type/class and an even wider spectrum of application spaces.

This focus on SWaP factors will never be more salient than in non-tethered applications, where a system’s performance, range, and reliability are all at the whim of the available power (though at the end of the day, everything in the world of electronics kind of is, right?). Non-tethered applications are the ones in which the system is not required to be connected to a fixed power source, such as AC power from a wall outlet (a.k.a., offline power source). Examples include anything mobile (from phones to vehicles), most forms of transportation (terrestrial or aerospace), tiny things (wearables and wireless sensor networks), and even the most untethered applications you can possibly find (space-based applications).

The amount of available power to a non-tethered system may be characterized in a number of different ways, but will invariably come down to a balance between power sources and the loads that consume them. As described in the first section, SWaP factors become so important in this application space because of the constant battle between allocating power for functionality (i.e., movement, data analysis, communication, etc.) and supporting the overhead of the system itself (i.e., larger mass consumes greater amount of the power budget). Such characterizations of power utilization will ultimately be the constraining, operational factor, whether it be called fuel (hydrocarbon-based combustion), battery-life, range, or flight time. The table below outlines many application-dependent considerations and their impact on SWaP-C factors.

An excellent strategy for optimizing system tradeoffs for SWaP-C factors is to take advantage of a family of components with a common footprint. This can allow for many advantages from flexibility ...