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super cheapo current limit

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spuffock

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An ordinary filament lamp makes a handy rough current limiter, with the extra benefit of some indication of fault current. As more current is drawn, the filament heats up and increases its resistance, further limiting the current that can flow. As an example of its use, I was handed a very complex logic board, and told that it blew the 5v rail fuse, but the short couldnt be found because it read about half an ohm from anywhere on the board. Replacing the fuse with a car headlamp bulb protected the power supply while allowing a few amps to flow into the fault. A quick dab around with a finger soon brought an ouch, and the defective chip was found.
 
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