PowerSource

Pity the poor laptop designer: Because laptops (or, by extension, any piece of portable equipment that uses a honkin' power-hungry Intel-type processor) must operate seamlessly from either an ac power adapter or a battery, the system power circuitry has to support a load that can vary from just under 9 to just under 17V. When the laptop is plugged into ac power and the system is sucking juice from the adapter, VDC can range up to a typical high of 16.8V. But when the laptop is running off battery power, VDC can range as low as 8.7V. Because the system has to support such a wide voltage range the power losses are heavy: Switching losses increase at higher voltages. Plus, the dc-dc switching frequency is lower (and thus efficiency) at higher voltages.

Intel realizes that if system architects seek to increase system speed and capability simply by following the existing system design methodoloy and cranking up clock speeds that laptop operating temperatures will shortly approach the surface temperature of the sun with a corresponding battery life in the milliseconds. So, the chip giant over the years has introduced a number of guidelines for improving power efficiency through system architecture. Enter Intel's Narrow VDC initiative, which seeks to lower power losses by shrinking the system load range. The strategy calls for replacing the battery charger circuit with a system-level charger voltage regulator, dropping the load the adapter sees down to 12.6V from the current 16.8V.

Majid Kafi, director of Intersil’s Notebook Power products group sees it this way: "This supports the battery [voltage] as powering the system bus and it requires much smaller voltage than traditional power scheme in the notebook." The total impact is 2-3% better efficiency. Not eye-popping numbers, but squeezing out more system power efficiency is done in dribs and drabs. For laptops with the highest power density batteries, this increase can result in up to 30 minutes extra of run time.

Are laptop manufacturers jumping all over NVDC? Not yet: Kafi says that so far one major OEM has switched to it, but the vendor has made the commitment of basing all its new notebook lines on it, and Kafi sees this as an industry trend indicator. Intersil is certainly hoping that's the case: It just introduced the ISL6257 Narrow VDC Battery charger controller  which Kafi believes is the first controller to reach the market that's optimized for NVDC. As laptop manufacturers see that there is no silver bullet, no new battery technology that's going to appear in the near future, picking up power efficiency in dribs and drabs will have to suffice. (That's right – don't hold your breath for cost-effective, energy-dense nanotechnology or micro fuel cells.)