By John Keller
Moore’s Law has been a blessing for computing, but it can be a curse for power-supply designers.
The tired axiom of the electronics industry, which roughly states that the transistor density of integrated circuits doubles every 24 months, is placing a set of increasingly crushing demands on power-component makers who must feed the right amounts of electricity to the latest generations of microprocessor behemoths.
Yet increasing demands for power in complex embedded military and aerospace systems is not the only force coming to bear on power supply designers. Along with providing ever-more power, they must design ever-smaller and lighter devices to satisfy industry demands.
Place an additional burden on power systems designers-the imperative to provide commercial off-the-shelf technology for a cost-conscious military-and something’s got to give.
“For our market, not only we are seeing power levels rising substantially, but we also are seeing a trend away from COTS and back toward customized devices,” explains Michael Henderson, director of sales and marketing at power supply maker Transistor Devices Inc. (TDI) in Cedar Knolls, N.J.
Henderson says TDI engineers are starting to realize that with increasing frequency the capabilities to provide the levels of power and electronic packaging sizes sufficient for today’s military and aerospace applications are simply not available off the shelf.
“That is causing more of a level of customization,” Henderson explains. “We are getting away from using off-the-shelf solutions because they don’t have the power densities that we need. We may be able to use some existing circuitry, but its definitely going more towards discrete.”
Several new applications and systems are emerging in communications and weapon systems that are putting a strain on power-generation sources such as engines, batteries, or generators, Henderson explains. “There is a limited amount of power generation, and we are seeing the gap really growing between the need and ability to supply power.”
Officials at other power companies also are experiencing this trend. “We are seeing a drive to reduce the size of the power component,” says Keith Nardone, senior manager of defense products at power supply designer Vicor Corp. in Andover, Mass.
“Designers of man-portable electronics, as well as aircraft, are interested in weight reduction,” Nardone says. “Devices must be small sized, have weight reduction, thermal management, and higher efficiencies. They are trying to put more electronics in a small space, so thermal management also is very important.”
Vicor engineers are attacking these applications demands primarily with the company’s V-I Chip, a factorized power architecture that deliver 75 watts input power per cubic inch in a surface-mount package.
“In some applications you can get away with using one chip, but in most applications it requires two chips, Nardone says.”This is still smaller than a typical quarter-brick power supply, which is 2.28 by 1.45 by 0.5 inch high.”
Dealing with heat has become a critical issue for power-supply designers-especially as they feel the pressure to reduce the sizes of their devices. “We are seeing more innovative ways of removing heat,” says TDI’s Henderson. “What we see is liquid cooling. A lot of these applications are on vehicles where we can tap into the coolant and radiator already on the vehicle.”
Liquid cooling, however, presents its own set of difficult challenges. Using a land vehicle’s radiator to cool electronics uses liquid coolant “that’s not really all that cool,” Henderson points out. The same can be said of surface ships using seawater for cooling while operating in the tropics where water temperatures can exceed 90 degrees.
Conversely, “sometimes the cooling liquid is too cold and you get a lot of condensation,” Henderson says.
In sum, however, demands for power are forcing power supply manufacturers and systems integrators to look at COTS in a whole new way. “Our customers have put a new definition on COTS,” Henderson says. “It is more of a “non-developmental item,” or NDI. If they can buy a product that currently exists or might require a slight modification, that is attractive to the customer.”