March 12, 2010
Lidow gives switching devices a GaN boost
By Bill Schweber

Maintaining that progress in conventional silicon-based MOSFET switching devices has reached the point of diminishing returns, Alex Lidow, co-founder and CEO of

Lidow's company is shipping enhancement-mode switches using this technology; depletion-mode switches, though easier to develop, are harder to use effectively, while enhancement-mode looks more like a standard MOSFET. The devices are targeting power supplies in server, data switches, hub, and even higher-power audio applications. Key to the cost-effective development is that these GaN-based devices, which are grown on top of silicon, can be built in standard CMOS fabs, and are thus priced like MOSFETs, not like GaN RF-signal transistors.

Packaging, also a key cost determinant for power devices, is also low cost with GaN, notes Lidow. Any heat sink (if needed) attaches directly to the die, since the process is self-isolating. Lack of a special package reduces thermal resistance, electrical resistance, and cost, of course.

Third-order Spice models are available for the GaN-based switching devices, along with reference designs and application notes, and are available via distributors. Lidow added that there are a few design-in differences when using this technology, which offers f_T of 2 GHz for the larger units and f_T of 5 GHz for the smaller ones: the GaN-based devices are fully enhanced at just 5 V, so you have to be careful you do not exceed 6 V at their gate. Noise and overshoot can therefore inadvertently trigger and turn on the switches, so it's the same design caution, once again: layout and attention to detail are critical. ♦

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February 25, 2010
It's all about battery power--and also energy
By Bill Schweber

Batteries are wonderful things. They use chemical energy to store, and then release, electrical energy (yes, there are some specialized, non-chemical batteries such as mechanical flywheel units, but that's a whole different story).

But it's not just energy, it's also about power. (Quick refresher here: power is the time rate at which energy is transferred or used.) And in batteries, both are important factors. When we look at product run times, we look at both the current consumption of the product, which relates to total energy stored, as well as power consumption, which relates to how fast the battery and its subsystem need to deliver and replenish that energy, and how fast the resultant heat must be removed. (More correctly, this current or power consumption should be looked at as dissipation, as the current and power are not "consumed"; they are turned mostly into heat–but the difference between those meanings is not the point here.}

Some of today's batteries have such high energy density (amount they can store per unit volume) that when they release it too suddenly--whether due to an internal fault or an external cause–they can develop and deliver enough heat energy to start a fire. It's very unnerving when your laptop PC, even if not plugged into an AC line or charger, starts to self-ignite, that's for sure.

Testing and abusing batteries for gross failure and resultant fires and explosion is a tough job, but someone's got to do it. Take a look at this recent article in The Wall Street Journal for a look at how Sandia Labs is doing it, "Where Batteries Go to Be Tortured". Sounds like real fun, I am sure many of us are a little jealous!♦

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February 20, 2010
Hang on to your hats, it's time for the APEC ride!
By Bill Schweber

This is the week of academia and industry's big

I won't be there, but several EE Times editors will, and they'll be looking for new products, topologies, tools, design ideas, and more. As they post their stories, I'll collect them here at the Power Management DesignLine home page so you can see them all in one place. ♦
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February 13, 2010
Are embedded LEDs the way to go?
By Bill Schweber

The venerable incandescent lamp is under assault–rightly or wrongly–as an inefficient blight on our environment (note: we're not discussing the validity of that argument here). Some incandescent opponents say that CFLs (compact fluorescent lamps) are the way to go; others say the CFL is merely a stopgap, and LEDs are really the way to go and CFLs are only an interim solution. My view is simple: I don't know what will happen or the "best" way to go, period.

But LED-based lighting certainly has some real virtues, which I don't need to detail for this audience, you know it all too well. I do think that the way we'll really learn about using LEDs for illumination, as well as ramp up high brightness LED (HB LED) production and experience, is to use them in dedicated, embedded applications, where there is no need to retrofit to exiting sockets, power-line control, switches, and related infrastructure or worry about compatibility issues.

For example, check out this battery-powered, LED-sourced work light called the Might-D-Light (and related products) from Cooper Industries. If it works as promised, it's a very good application of HB LEDs. And since it is self-contained, there are no issues related to the LEDs being compatible with existing bulbs (incandescent, halogen, or other standard types).

Products like this take advantage of HB LEDs while not being subject to the challenges and stress of mass markets and the broad spectrum of user understanding, while working out high-volume issues, spurring engineering expertise, and developing mass-production. That's the way to go, it seems to me.♦

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