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Power Play for USB

One of the worst things about upgrading your cell phone is that you lose all your accessories, such as the car charger/ adapter for the phone. Such was the case recently when I upgraded to a Motorola Q and my wife to a Motorola KRAZR. But to my surprise, the power connector for both was the familiar USB mini connector.

This is not to say that I had a USB car charger on hand—I do have to purchase one. But they're easy enough to find, and inexpensive, too, selling for about $10. What's more, if I buy two—one for each car—I no longer have to worry that the right adapter is in the right car. I don't know if all cell phone makers are employing the mini USB port for power, but it would be great if they did.

Naturally, there's more to the story. I looked at the back of the AC adapter that came with the phones and noticed that the output is 5.0 Vdc at 850 mA. This got me thinking about the SIMPLE SWITCHER evaluation board that I got from National Semiconductor and wrote about in the February issue. The output for that board is 5.0 Vdc at 3A. And it's just sitting on my workbench with nothing to do. Also sitting around in various places are USB and cigarette lighter connectors/cords.

Here's what I'm thinking: Wouldn't it be great to have one device that handles car, AC and battery charging for the cell phones. I could take any of the old AC adapters I have lying around, connect it to the board and get 5V out. Also, if I took four AA rechargeable batteries, I could connect them to the board and get a regulated 5V out. Finally, I could connect a cigarette lighter connector/cord to the board as well.

All that's missing, I think, is the pinout for the USB mini-connector, so that I know how to connect the USB cord to the 5V output. I found this information easy enough on the web in the USB Wikipedia at So that's it, I think. E-mail your comments to me at [email protected]


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