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June, 2016
The Advantages of Digital Signal Processing in Power Converters
By Jeff Elliott T
he power electronics industry is increasingly moving from analog to digital power convert- ers, particularly when high-density power
output is required. Many mission-critical opera- tions in aerospace and defense, as well as in some industrial applications, require output power in the multi-kilowatt range. Given the nature of these applications and the rugged conditions in which they must operate, these converters must also withstand strong vibration, shock, EMI, humidity, and other environmental effects without breaking down. “You generally don’t just go to a catalog and
pick out something that’s going to provide you with 50,000 watts of power,” says Kamran Kazem, vice president and CTO at Magnetic Design Labs (MDL). “Almost everything is custom-made in that arena.” The California-based company designs and manufactures analog, digital switching and linear power suppliers, DC-AC converters, and DC-DC converters.
Digital vs. Analog According to Kazem, digital power devices are
capable of operating over a wide operating range, require few external components, are easy to com-
“The main reason to go with digital over analog is that almost anything can be customized fairly easily with just a little bit of code.”
municate with, and introduce a degree of flexibili- ty in control not previously available with analog techniques. “The main reason to go with digital over analog is that almost anything can be cus-
MDL Digi-Sine inverter DSP control board showing DSP Chip.
Digital signal processing (DSP) is also more
precise than analog. Settings do not drift with time and temperature changes since they are controlled only by the DSP’s clock and the software, not by cap or resistor values that are susceptible to change. One important feature of a digital converter
is its flexibility. Digital Power converters offer an array of programmable parameters, including out- put voltage settings, output current, current limit trip point, power sequencing routines, voltage margining, and multiple thresholds for warning and fault conditions for over-current, over-temper-
tomized fairly easily with just a little bit of code,” says Kazam. “With an analog type of converter, once it is designed, it is rather difficult to change or get any additional information from it, and there is no real-time communication.”
ature, and under- and over-voltage. Fault condi- tions and power usage can also be stored in non- volatile flash memory for later recall. Designers can program any of these parame-
ters at any point during the product’s lifecycle. These, and other function or feature changes, often simply require updating the flash memory, and can even be updated remotely over the internet. With analog, similar parameter or function changes require hardware adjustments and often also require an entirely new PCB. Real-time communications for monitoring
and diagnostics is another major benefit. Digital power conversion devices can be tied into existing networked systems as well as communication processors and the information used to monitor and control the output. Despite these and other advantages of DSP
technology, for most engineers the biggest downside is the learning curve that the technology demands. “It takes a high skill level and advanced edu-
cation to successfully design for digital control of analog signals using a DSP processor,” says Kazem. “Designers who are used to working in the analog domain can get into a sophisticated DSP application and find that it takes too long or becomes too difficult to complete the work.” Despite excellent programming and debug
tools from DSP chip vendors, the tools themselves can be difficult to use for the inexperienced designer.
Hi-Rel Applications In addition to DSP, many mission-critical
electronics used in military and aerospace applica- tions must be designed to satisfy strict ruggediza- tion and high-reliability requirements. Hi-rel is measured by a device’s probability of
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