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Topic: Help please (Read 99 times) previous topic - next topic

paulw2

Hi. Need help please...
Why would my mega work fine when powered from usb. But it burns regulator when connecting to a 12vdc supply through the jack?

TheMemberFormerlyKnownAsAWOL

Because you're wasting seven volts at whatever current you are drawing.
Please don't PM technical questions - post them on the forum, then everyone benefits/suffers equally

paulw2

Nope. Its rated for 12v

ballscrewbob

Despite the rating a lot of us run around 8-10 volts so the regulator has less voltage to dissipate as wasted heat.

Some cheaper or older PSU's "spike" when turned on which is hard to see on a multimeter but easy with a scope.

It may not be the answer you were looking for but its the one I am giving based on either experience, educated guess, google (who would have thunk it ! ) or the fact that you gave nothing to go with in the first place so I used my wonky crystal ball.

sterretje

#4
Mar 01, 2020, 10:19 am Last Edit: Mar 01, 2020, 01:24 pm by sterretje
Nope. Its rated for 12v
I think you misunderstand. The voltage regulator brings the input voltage down from 12V to 5V. The board draws roughly (thumbsuck, never measured it) 50 mA. So the regulator needs to dissipate 350 mW (7 x 50) and will happily do so.

Once you start powering other stuff from the 5V pin, you somewhere reach the limit if what can be dissipated and the regulator will overheat.
If you understand an example, use it.
If you don't understand an example, don't use it.

Electronics engineer by trade, software engineer by profession. Trying to get back into electronics after 15 years absence.

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