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Recognizing right power priority

Posted: 18 Mar 2010 ?? ?Print Version ?Bookmark and Share

Keywords:low power? battery-powered application? MOSFET?

These days you can't look at a data sheet or design and not see Low Power, usually fairly high in the "features" section. Everyone likes low power, and why not? All other things being equal, low power is either a must-have or a nice-to-have attribute, and hardly ever a not-needed one. But it is important to step back and ask why you favor low power, and the implications of going low power.

For battery-power designs, lower power means more operating time before the batteries must be recharged or replaced. Even a modest 5 percent or 10 percent decrease in consumption is usually worth the cost, depending on the application or market, of course. In contrast, for AC line-operated products, lower power operation really plays out in thermal dissipation issues more than power-source issues, since another few watts from the line is usually not as big a deal as reducing internal heating, and thus cooling requirements, in the box. In fact, a few milliwatts saved in a line-operated device is usually insignificant. And for big applications, such as running a multi-horsepower motor, a few milliwatts saved is usually meaningless, unless it means that a smaller MOSFET driver can be used, or a driver heat sink will be unnecessary.

Low power usually saves money, but not always. Before you rush to put that low-power IC on your BOM, ask yourself the eternal, basic engineering questions: Why am I doing this? Is the "pain" worth the gain? What are my priorities? What are the tradeoffs and downsides, if any, of going this route? Will I be unnecessarily limiting my list of approved vendors?

Then you can make an informed decision, without going the low-power route just to be trendy and have a nice PR statement. It wasn't that long ago when consumer multimedia amplifier in "stereo" systems boasted, right on their front panels, that they incorporated 1bit DACs, as if that would impress the customer. And where are those boasts now?

- Bill Schweber
Power Management DesignLine

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