Design Con 2015

Power supplies go digital

-February 13, 2013

Digital control inside an on-board power supply facilitates improved efficiency, reduced total cost and advanced system power management. The following is from an Ericsson white paper and is very relevant to Digital Power.


Digital techniques in power conversion


The concept of “digital power” has received significant attention and promotion in the past few years, from both semiconductor suppliers and power supply manufacturers. There is a need to explain the concepts of digital power; explore the advantages and tradeoffs of digital techniques compared to analog approaches; discuss some of the standardization directions; and explore the possibilities for digital power.

Digital power is defined and implemented differently by various suppliers; moreover, there is not yet an appreciable field history of successful large-scale designs using digital approaches. The result is an atmosphere of uncertainty and some confusion about digital power. Is it cost effective? How does its performance compare to conventional analog approaches? Is it reliable? Does it affect the complexity of the design and development process? Are developers with specialized skills needed? How “standardized” is it and will it affect second sourcing?

A more proactive stance is needed in defining the process to enable the implementation of power supplies and systems using digital power. Most importantly, the above questions must be answered so that the end user – a system integrator or original equipment manufacturer (OEM) – can work confidently with digital power.

Why is power conversion still mostly in the analog domain? The main reason is that efficiency is vital for most power system applications. No matter how many “bells and whistles” going digital might add, if it detracts from efficiency it will have limited appeal. The added power dissipation “overhead” in the form of additional circuitry for digital controls made this approach quite unattractive until very recently.

Cost and packaging density are also issues. Happily, the advent of a mature complementary metal oxide semiconductor (CMOS) digital technology has solved these issues by providing digital processing with high density, negligible power dissipation at low cost.

Digital control and management

“Digital power” is a broad term that encompasses several concepts and subdisciplines, and the end user can benefit from digital power on several different levels. One of the major features of digital power is that for any given system application, the end user will typically select only a subset of the available digital power solutions. This decision will be based on factors such as cost, complexity and system availability and maintenance requirements.

One key concept is the distinction between power control and power management. The term “power control” is used to address the internal control functions in a power supply, especially the cycle by-cycle management of the energy flow. Note that a power supply using digital power control techniques will appear identical to the end user as a power supply using analog power control techniques.

The term “power management” is used to address communication and/or control outside one or more power supplies. This includes functions such as power system configuration, control and monitoring and fault detection. Presently, these functions tend to be a combination of analog and digital. Digital power management implies that all of these functions are implemented with digital techniques and some type of data communications bus structure.

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