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Old 06-09-2008, 10:47 PM   #13 (permalink)
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Join Date: Jun 2008
Location: NC
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Cxy Hatch - '92 Honda Civic CX

0ftlbs - '05 Honda S2000
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Originally Posted by dcb View Post
With the standard LCD we are barely at 1/5 the capacity of the regulator.

At ambient room temperatures maybe. Our end goal has this device powered by a 13-14V alternator inside a hot car. 14V * 200mA is 2.8W (LDO). We only use 5V * 200mA = 1W . That's 1.8W burned in the regulator.

The way I have mine mounted is non heat sinked with no airflow. I admit I've got it in a project box pretty sealed up which isn't the best idea. Its 100 degrees ambient this week (~36C , North Carolina) not counting any solar loading.

Max junction is 125C with a RthetaJA of 65 C/W. Using the above 1.8W*65C/W = 117 C. You can see if our 200mA is correct we are already in violation of the max temp even under a 25C air conditioned lab when using the cars voltage range. Anyone got some good temperature probes at home to mount to one of these? I'll take the board into work tomorrow and try to get some load current measurements.

I plan to mount a nice sized power resistor in front of the 7805. It will help current limit and burn some of the initial 14V .
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