Touch screens, amplifiers, energy-harvesting and lithium ion batteries

-January 05, 2009

I caught up with my trade paper reading over the holiday and have a whole slew of things from Electronic Products. Most of these were done by someone who works for a company trying to sell you stuff, but they still are pretty interesting. Bruce DeVisser from Fujitsu has a nice overview of touch-screen technology. Bob Kratas of Cirrus Logic discussed amplifier topologies like class AB, class D and class H, where the power rail is adjusted on a class AB as the signal strength varies. Paul O’Shea, the Electronics Products staff writer has a nice blurb about an energy-harvesting module by Advanced Linear Devices, a great outfit right here in Sunnyvale. Finally there were two articles about lithium ion batteries. George Altemose from Aeroflex talks about balancing cells in batteries. As my buddy Dave found out after swelling two cells in his $1600 lithium polymer battery packs, cell balance is essential for lithium ion batteries to work in cars. Tesla has quite a job balancing 6800 cells. On that same track, Jim Douglass from Linear Technology has a good article about battery management issues in hybrid electric vehicles (HEV). Jim is talking about Linear Techs LTC6802 battery stack monitor. It is a really cool part, check it out. (I wonder if the analog folks at LT realize 6802 is an old microprocessor part number?).

You can tell Linear Tech has been working on battery monitors since my electronic flea market buddy Fran Hoffart has a great article about extending the life of batteries in the September 2008 Linear Technology Magazine (4meg pdf). Since LT has to come up with the silicon to manage these troublesome beasts, they don’t tell you marketing hype like “up to 1000 charge-discharge cycles”. Fran lays out the grim reality—if you deep cycle them, or run them at temperature extremes lithium ion cells hold less than the rated charge. If you want to know how persnickety lithium ion batteries are, look at figure 3 that shows how you only get 85% charge if you float the batteries at 4.1 volts instead of 4.2. But don’t leave them floating forever like you do with lead acid, that damages the cells and will reduce capacity as well. That is why you are supposed to store your laptop with 60% charge or less.

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