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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February 07, 2010
When a solution is the solution, or: when an old dog meets an old dummy (load)
By Bill Schweber

Like most engineers, I have used dummy loads spanning DC through RF, and from a few watts to hundreds of watts. Most of these loads were built up from basic resistors, and in some cases special heat-sinking was needed to keep things under control. I fondly remember building a 1-kW, non-inductive RF load where the dissipative element was housed in a one-gallon paint can filled with mineral oil, to keep it from overheating as it would have in free air (yes, active forced-air cooling was another option, but that approach brought a new set of problems).

But sometimes, when you think you have seen it all, you haven't. I came across a fascinating article n the January 2010 of Power Electronics Technology, entitled "Testing Power Converters Using a Liquid-Rheostat Dummy Load". This article is not academic-theoretical or merely speculative: it has full analysis, rationale, construction details, performance graphs, and reference information on how to build and use an electrochemical cell as a dummy load. This is clearly a case where A solution is THE solution, so to speak. Apparently, this type of dummy load is not new at all (and how often do we even see the word "rheostat" in our electronics world?).

The other thing I found interesting was that the load in the story was not for some extreme power raring. Instead, it was for a 3.3 V, 40 W (continuous) output, which is a fairly modest power level. The conventional alternatives, according to the author, were too costly for his modest budget, and also would have required a complicated switching arrangement to set different test-loading levels, which would add undesired inductance and additional cost.

I'm not saying the liquid rheostat is the answer to you problems, But it's an interesting alternative, and interesting in itself as a creative solution (there's that word again!) to a specific test challenge.

Note: the two modest equations in the article did not show up in the online version–I saw the article in that ancient medium of print, where they did appear–so here they are:

R = (ρ × L)/A

R = d/(δ × A)

Enjoy getting out of your dummy "comfort" zone!♦

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