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Power dissipation questions

(1) How long can a standard alkaline AA battery go with a voltage of

1.5V running a device that is rated 1.5V, 10W?

I read somewhere such a battery was rated at 150mAh. Which means (150 x 0.001 x 1.5) = 0.225W upto 1 hour. So if my device is rated at 1W, it will last 15 minutes with one alkaline battery?

(2) Individual ICs and transducers are rated at their maximum power dissipation. Does this change alot with temperature, for example an SDRAM memory IC chip?

(3) Where can I find information on the power specs of LCD panels? sharp sanyo do not rate their panel modules, and earthLCD doesnt even provide the specs.

Reply to
Ghazan Haider
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Others have handled the battery. Here, if you look closely, you will find the devices power handling is rated at a particular max. junction temperature. You will also find a specification for thermal resistance from junction to case, from which you can derive a case temperature for the junction temperature. After that things depend on how you dissipate the heat from the case. If the case temperature is already at the specified junction temperature, the power handling capability is zero.

The key value is that junction temperature. However it does not specify the absolute max (you might be cooling it with liquid hydrogen) which in turn might depend on wire sizes connecting to the pads, or connections in the metalization layer, or whatnot.

--
Chuck F (cbfalconer@yahoo.com) (cbfalconer@worldnet.att.net)
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     USE worldnet address!
Reply to
CBFalconer

I got the 150mAh from a googled up website. Its been corrected in my notes now.

The 10W comes from an x86 MCU I was hoping to use. I now think considering other pieces of the puzzle, using an ARM will be more feasible. That should bring the total wattage to a little under 1W, maybe 1-3 hours usage. With the x86 CPU and graphics chip, it came up to 10W.

So I gather theres the (1) driving circuit (2) panel itself (3) backlighting on some. The most power is obviously taken by 3, then 1, and almost none by 2.

I wonder if they make QVGA panels but with pixels that are similar to calculators digits, with back reflections. Cant produce pics, but will make a nice linux computer, possibly running X with a good browser...

If i can make this run for upto 10 hours on 2-4 AA batteries I'm golden.

Reply to
Ghazan Haider

Do not forget that the faster you discharge the battery, the less you get out.

Reply to
Neil Kurzman

Forget it. It's essentially impossible to get x86-class CPUs of any current type that would run off a single battery for long enough to be worth considering. You either need considerably more batteries (--> a notebook accu pack), buy thousands of them (notebook CPUs are essentially unavailable in small quantitities) or use an entirely different class of CPU.

Yep.

Of course they do. They're used in all those PDAs. The device you're talking about designing is, essentially, a re-invention of that form factor. More to the point, you're in the process of re-inventing the Zaurus.

--
Hans-Bernhard Broeker (broeker@physik.rwth-aachen.de)
Even if all the snow were burnt, ashes would remain.
Reply to
Hans-Bernhard Broeker

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