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Topic: 3.3 DC current for Uno and Mega 2560 (Read 7 times) previous topic - next topic


Is there a reason that specs on Hardware page say that maximum current for 3.3 DC pin on Uno and Mega 2560 is 50 mA not 150 mA? Using LP2985 as 3.3V regulator should provide 150 mA...

Since this is my first post ;) I can not add links to hardware pages :) but on both is:
DC Current for 3.3V Pin      50 mA



You have to worry about power dissipation as well as current.  Here's what Gianluca has to say: "With 150mA of load at 12V the regulator will go in thermal shut down (or burn) because it will dissipate 1.3W instead of the 0.45W it could not exceed without a proper heat sink

At  12V it could easily provide 50mA (75mA @ 9V)

it is the same for the Mega2560"


Thank You for a clarification. That makes sense.


Um.  The 3.3V regulator comes AFTER the 5V regulator, so it would never dissipate more than about 0.3W regardless of input voltage to the board.  (now, the 5V regulator could get in trouble, but it's still spec'ed at a much higher current.)


The dissipation at 150mA assuming it comes after the 5V regulator is 0.15*(5-3.3)=0.255W.
Seeing that the max dissipation at 25C is (125-25)/225[ch8776]0.444W (calculation from datasheet), you can safely pull 150mA.

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