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I'm using 9v regulator (l7809cv) with 12 1,5v AA batteries in series so that my application gets both 18v and 9v for my Arduino Uno r3 board.
I've been running it for about 15min without any problems, but when I touch the l7809 it feels really hot after 10min or so.
I've measured a current between the batteries and the l7809 to be steadily around 100mah. I haven't exceeded the maximum voltage input ratings, and as far as I can see, neither the current ratings (it says in the datasheet that it's "internally limited")
Maximum temp. appears to be 0 - 150 celcius, which seems to be more than enough.
So my question is, is it OK that the component gets so hot that it hurts touching it although it probably isn't 150 c, or should I make some kind of heat sink for it?