Yes.  This is expected, unless you're drawing really low current.  Just a=
dd a=20
decent heatsink.  The usual 7805 will protect itself (by shutting off) if=
 it=20
overheats.

Since you mention cascading, I have this situation frequently and instead=
 of=20
adding a (relatively) large heatsink, I use 2 regulators in "series" -- a=
=20
7810 to drop the 13.8V to 10V, then send that to the 7805 to drop it to 5=
V. =20
Cost is another 35c or so for the 7810 regulator.

Cheers,
-Neil.


On Friday 14 May 2004 07:39 am, Lucian scribbled:
> Hello,
>
> I might be disturbing you with a very simple question, but I ran out of
> solutions for this problem.
> I have designed a power supply which gives 13.8V, with the adjustable
> LM338, and tied to the output, the input of an LM7805, in order to
> obtain 5V also (I need both 13.8V and 5V). Is it ok to do this ? Becaus=
e
> when I power the board, the 7805 gets very hot quickly and I had to pul=
l
> it off (there is no power consumption as I haven't planted all the IC's
> yet).
> I am wondering what could be the cause of this, as all the connections
> are ok.
> Please give me a suggestion. Thank you !
>
> Lucian

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