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Possible Duplicate:
My linear voltage regulator is overheating very fast

I have a task to develop a mobile charger from 12 Volt DC power, now i have decided to use LM7805 for that.... but my problem is ...when i connect LM7805 to directly to the 12 Volt DC power supply ........ It GET HEATED MUCH.....EVEN I CAN't Touch it with my bare hand.... what should i have to do ...to get rid of it.... though hit sink is one solution but i don't want to try it...i searching for some other solution. NOTE:i didn't use any other electric component other than LM7805....

Thanks....

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  • \$\begingroup\$ electronics.stackexchange.com/questions/11625/… \$\endgroup\$ – Kellenjb Dec 27 '11 at 15:42
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    \$\begingroup\$ electronics.stackexchange.com/questions/18478/… \$\endgroup\$ – Kellenjb Dec 27 '11 at 15:42
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    \$\begingroup\$ The regulator in the 2nd question I linked isn't exactly the same one that you are using, but it is a form of the 7805 so should be close enough for you. \$\endgroup\$ – Kellenjb Dec 27 '11 at 15:47
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    \$\begingroup\$ When you say "i didn't use any other electric component other than LM7805" are you saying you didn't even hook up the IC the way the datasheet says to (with capacitors)?? Or are you saying you just haven't hooked up any load to it yet? What is the voltage out that you are seeing? \$\endgroup\$ – Kellenjb Dec 27 '11 at 15:52
  • \$\begingroup\$ Why the hell people don't search before asking? \$\endgroup\$ – abdullah kahraman Dec 27 '11 at 16:02
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If you don't have any load connected, then it sounds like you have the pins on the 7805 mixed up. If you get the input voltage and ground reversed (or output voltage and ground, or input and output) it'll pass a lot of current, and heat up.

Check the datasheet for your specific 7805 to check the pinout; for example, page 2 of this 7805 datasheet. There may be a few different pinouts (I've seen In / Out / GND ; though not certain if that was a LM7805 or a different part number).

If you do have load connected (more then a few 100mA), follow the advice of everyone else.

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