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Need help: Transistor 7805 problem


Hello . I just make a PSP charger.
I used a 12v,450mA adapter as power source and a 7805 transistor to get 5v output.
this is the wire map: http://i247.photobucket.com/albums/gg132/chipmapple/untitled-38.jpg

When i plug it to my PSP, it's work, but the Transistor start become hotter, after 2mins the transitor is very hot...
I don't know what's wrong with it, i tried other 7805 but got same problem.
Please help....
Thanks very much .!
*sorry for my bad English

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dudenr336 years ago
Try this circuit:
http://www.mikrocontroller.net/articles/Datei:V_Regler.gif

Then see if the problem still occurs.
I assume that you've already checked you have the pins in the correct order, right?
aankun dudenr336 years ago
I follow the circuit you give above, and now the diode is hot. Is it normal???
dudenr33 aankun6 years ago
No, its not. Have you paid attention to the polarity? If you placed the diode in the wrong direction, you shouldnt get any power at all. Does the rest of the circuit work properly?
Goodhart6 years ago
Some other things to consider would be making your power supply a little more "regulated" by incorporating a few other components....see my schematic below:
7805_12v Larger.jpg
login721 (author) 6 years ago
Thanks,! i ll try it.
The component you are using is a voltage regulator, not a transistor.

Linear regulators, like the one you are using are only 65% efficient, so a lot of the energy going through it is converted to heat.

The regulator is designed to only handle 1A, but the charging current should be less than this (check it with a meter to make sure), so it would be normal for it to be this hot. The best solution is to screw it to a piece of aluminium or copper plate as a heatsink.
The efficiency being a function of voltage drop of course.