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Digital Power Quickly Goes from “Nice Idea” to “Absolutely Necessary” Architecture


by Bill Schweber for Mouser Electronics J • •


ust a few years ago, “digital power” was mostly a concept with some prototypes under long-term evaluation, but few actual installations. Fast- forward to 2016, and you will see these supplies are now standard and essential in power-intensive


applications such as data centers. Without the attributes and virtues they offer, it would be very hard to provide the hundreds of amps at a variety of DC rails given the space available, the efficiency mandates and thermal constraints, and the sophisticated supply demands of these installations. The reasons for the widespread adoption of digital


power supplies in these power-intensive applications include: •


Their high efficiency yields lower operating cost; there is less heat to dissipate; and they make it easier to meet environmental-related regulatory requirements.


They can implement the challenging and sophisticated technical requirements of powering processors and FPGAs.


Their flexibility supports dynamic changes in strategies during operation, and they can handle complicated power-up and power-down sequencing scenarios. Power-supply designers (and many users) are generally


a cautious group, as they must be when dealing with high current, voltage and power levels, and the consequences to equipment and people of supply malfunction or failure. It is a cautious user base that prefers products with a track record and long, viable product life spanning a decade, two decades, or more, and that does not want to subscribe to a trend just for sake of being leading edge. For these and other reasons, there was some early reluctance to embrace the firmware-based approach, but the situation has changed. However, due to the positive track record of high-end digital power confirmed by solid data, other application areas, such as industrial systems, are seeing “trickle down” availability at lower levels. The gains


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include improved efficiency from low load to full load, which saves energy, reduces thermal stress on components, simplifies cooling challenges and increases MTBF (mean time between failures).


What is “Digital Power?” The objective of a power supply or converter is simple to state: provide a stable, regulated DC output at the desired voltage value despite changes in input voltage or load conditions. This requires some form of closed-loop control within the DC/DC converter, based on measurement of the actual output voltage, comparison with the setpoint value, and implementing feedback-based corrections to force the output back to the setpoint and keep it there. This regulation has traditionally been implemented using a closed-loop negative-feedback with analog circuitry in a switching regulator, Figure 1. (The alternative, a low-dropout regulator, or LDO, is also an option, but only viable at fairly low power levels.) There are many standard architectures for these switchers, with a long list of additional enhancements to increase efficiency across the entire load range, boost performance and ensure consistent operation. These enhancements can become quite complicated and clever, and have impressive names such as SEPIC (single-ended primary-inductor converter). These variations can become fairly complicated and sophisticated, but all have one drawback: they lack


Figure 1: The standard analog power converter uses the


well-known closed-loop topology to maintain a regulated DC output despite changes in input and load.


www.mouser.com January 2017


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