using a step down converter would be more efficient for sure, but if 24v
is within the spec of the 7805, this should work.
if you're getting into problems with power dissipation (or if 24v is too
much for a 7805), you could use a 7815 and a 7805 in series, to spread
heat production over two devices. so you might eventually be able to get
rid of heat sinks.
tino

************************************************************************
******************************


>-----Original Message-----
>From: piclist-bounces@mit.edu [mailto:piclist-bounces@mit.edu] 
>On Behalf Of phil B
>Sent: Wednesday, June 22, 2005 8:25 PM
>To: Microcontroller discussion list - Public.
>Subject: Re: [EE]: can I use 7805 to step down 24V to 5V?
>
>
>Probably.  The input voltage within spec but you don't
>say current requirements.  You will dissipate the
>different in heat so I'd be conservative on picking
>the package and be prepared to use a heat sink.  
>Linears like the 78xx family are pretty inefficient
>but if that's not an issue you will be ok.  Also,
>calculate the additional drain on the 24V supply.
>
>
>--- John Waters <john_fm_waters@hotmail.com> wrote:
>
>> Hi All,
>> 
>> My circuit needs both 24V and 5V, but I have only a
>> single 24V supply. Is
>> there any way to step down 24V to 5V? Can I use a
>> 7805? If this is not a 
>> good way, any better alternative?
>> 
>> Thanks in advance!
>> 
>> John
>> 
>> 
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