With most of the 7805 and 7905 chips the more voltage you pump into it the
hotter it will get.  IE I can pump 16 volts into a 780f with practicly no
drain and it will get hot to the touch.   However I can pump 9 volts into it
and it gets only warm.  Not all the regulators do this.   Mostly the cheap
ones.


----- Original Message -----
From: "fred jones" <boattow@HOTMAIL.COM>
To: <PICLIST@MITVMA.MIT.EDU>
Sent: Sunday, March 09, 2003 9:43 PM
Subject: [OT]: 7905 getting hot!


> Hi all,
> I thought I'd ask this question here as my pool of friends here can't seem
> to offer any help.  I have a circuit where I am feeding -24V into a 7905
> linear regulator.  It gets very hot, can't keep your finger on it.  It is
on
> a pretty hefty heatsink.  I took the output leg loose and measured the
> current draw its supplying and it shows to be 280ma.  I would think that
it
> should not have any problem with this and shouldn't be getting hot.  I
> thought maybe it was getting so hot because there was such a large voltage
> feeding it so I then took the circuit off of the 24v supply and fed it
with
> 12V and again it still gets too hot to touch.  I had a .1uf cap on the
input
> and output.  I looked at the data sheet and from that I tried changing
them
> out to a 2.2uf on the input and a 1uf on the output.  At the same time, I
> chaged out the regulator to one of a different brand.  Still the same
> results.
>
> My questions would be should it be getting that hot?  I thought that it
> shouldn't at only 280ma.  If not, can you point me toward any problems I
> might be having that could cause this?  Suggestions of things to look at
> would be greatly appreciated.
> Thanks,
> FJ
>
> _________________________________________________________________
> The new MSN 8: smart spam protection and 2 months FREE*
> http://join.msn.com/?page=features/junkmail
>
> --
> http://www.piclist.com hint: The list server can filter out subtopics
> (like ads or off topics) for you. See http://www.piclist.com/#topics
>

--
http://www.piclist.com#nomail Going offline? Don't AutoReply us!
email listserv@mitvma.mit.edu with SET PICList DIGEST in the body