Archive for September 13th, 2012
Current-Sense Resistors: Mind the Power
Posted by Ed in Electronics Workbench on 13-September-2012
The bench supplies I use have current limiting, but the 10 mA meter resolution leaves a lot to be desired and I conjured up a simpleminded 200 mA meter from a panel-mount meter and a 1 Ω sense resistor. That means it’s good for only 200 mA, so I insert it in series with the supply only when it’s needed. Lately it’s been reading more than a little bit high and I took it apart to find this obvious evidence of abuse:
Homebrew millammeter with burned sense resistor
The loose resistor sitting atop the chip shows what the burned resistor soldered in the circuit should look like.
The power supply has a 3 A current limit. No surprise: 9 W is more than the unfortunate 5 W resistor can handle.
It’s all better now …
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