The Future of Redundant Power Supplies: PMBus


There are many potential benefits that a 100% digitally controlled redundant power supply can offer, including improved efficiency, reliability, and flexibility, so it may seem strange that the majority of power supplies in the market today function using controllers that communicate based on many basic analog protocols. This however, is primarily due to the lack of a suitable, industry-wide standard for digital power management. While manufacturers have made efforts to implement fully digital controllers for power supplies via add-ons from proprietary architecture, the lack of a trustworthy, universal standard had hindered the growth of the digital controller industry until the introduction of the PMBus.
Power management bus or PMBus is a free, fully digital, and open-standard power-management protocol with a fully defined and refined command language that was developed to work over a physical bus with almost any power conversion device. So PMBus effectively offers a more efficient way for power converters to communicate with one another. This protocol was meticulously developed by a group of semiconductor manufacturers that aspired to quell the industry’s lack of a universal standard for digital power management.

One of the benefits that make the PMBus so useful is that it allows users to alter a power system’s parameters in the field or during factory testing at any time without having to perform hardware modifications. A majority of these changes can be made using very simple software updates or by making one-time parameter changes to the converter. This allows users to engage with the redundant power supplies in new and useful ways that were not at all commonplace before. For instance, when using power supplies that do not utilize PMBus protocols, users are often unable to determine what issues cause catastrophic rackmount chassis level system failures until it is too late and a power supply has already crashed and needs to be replaced. With the PMBus however, according to a report from Emerson Network Power and Intel, “The latest version of the PMBus protocol extends the already comprehensive feature set of the standard, to include real-time value reporting of ac input voltage, current and power to within 5% accuracy at very light loads.” This means that users will be able to essentially monitor the functions of their power supplies and make changes accordingly to prevent catastrophic failures that often occur due to power supply malfunction.

Additionally, with PMBus integrated digital power supply control, it is possible to create non-linear control loops that limit a power supply’s compensation based on its operating functions. Essentially, the power supply can become adaptive in nature, capable of exhibiting fast response times when it is essential to the equipment or system the power supply is powering, and slower response times for less essential applications. In this way, PMBus is somewhat capable of making power supplies more efficient. While it cannot actually improve a power supplies ratio of energy consumption to energy waste (i.e. efficiency), it is a crucial component in making the power supply “smarter” for the job.

This range of flexibility is revolutionizing the power supply industry, and now that the PMBus is making gains in popularity, you can expect to see many more power supplies that feature PMBus control in the coming years.

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