Cell-phone charger: nice idea, bad implementation

-November 26, 2012

Now and again you come across a device that’s so simple, useful, and functional that you’re glad to add it to your already-overladen workbag; that is, until it breaks, for the dumbest of design reasons. In this case, I am talking about a cheap USB power connector.

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I got one of these devices a while back. It’s a simple cell-phone backup battery from a no-name Chinese company that was a show giveaway from a well-known IC manufacturer. While the idea was good, from a marketing standpoint, it’s ironic that no parts from that company can be found inside. Instead, the main part comes from Texas Instruments, in the form of the LM324 operational amplifier, along with a USB power detector and battery-charging circuitry.

I may need your help ID’ing some of the other components, but a hulking—relative to the size of the board—inductor, as well as a 220-μF, 16V electrolytic capacitor tell me that U1 (labeled DK J8) may be the output transistor for a low-frequency switching power circuit.

In any case, it’s a classic case of a useful device gone bad: A poorly designed mini-USB input power port came detached right when I needed it most. Now the device is useless, unless I can get it soldered on again. Given the size of the solder positions and their location under the connector, a fix does not seem likely. Suggestions for how to do that are welcome. For now, it’s an interesting lesson for anyone who thinks the MCU or processor is the most important part of an advanced system. All reverts to naught when the connector breaks!

How often have you seen good devices or designs fail because of silly corner-cutting? Send your photos and story to patrick.mannion@ubm.com; we have to do a collection of these!

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