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Power supplies

Digital power techniques threaten analog power-supply obsolescence

January 02, 2011 | Patrick Le Fevre | 222901998
Digital power techniques threaten analog power-supply obsolescence Patrick Le Fevre, Director of Marketing and Communication, Ericsson Power Modules, suggests that power-supply engineers need to reconsider their design approaches as digital power techniques start to threaten analog power-supply obsolescence.
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Following decades of development, top-specification dc/dc converters have arrived at a performance plateau that requires power-supply engineers to reconsider their design approaches. In effect, converters that use familiar analog control schemes are now incapable of making anything but very small improvements in terms of the conversion efficiency and power density metrics that traditionally drive designers choices. As a result, digital power control techniques are rapidly gaining market share as designers increasingly appreciate the advantages that the technology offers over its analogue counterpart.

In reality, any digital power converter employs a combination of analog and digital circuitry that mixed-signal silicon processes make possible. In this context, digital power control refers to implementing the inner control loop of a power converter with digital circuitry rather than using analog schemes.

For the simplest example of a buck converter, this means substituting an analog-to-digital converter for the conventional error-signal feedback amplifier and controlling the pulse-width modulator that drives the power switches using digital-signal-processing techniques in place of a voltage reference, ramp generator, and comparator, Figure 1:

Figure 1. A digital buck-converter substitutes digital-signal-processing techniques for the familiar analogue control loop.

Given a mixed-signal core, its hugely attractive to add on-chip digital power management functionality that consists of supervisory and control circuitry that can communicate with external logic to facilitate power management schemes. At negligible additional silicon cost, integrating such functionality slashes PCB real estate requirements while optimising the coupling between the power converters core and its measurement and control subsystem.

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