Max output of 7805
Can anyone tell me what the maximum current output of a 7805 is?
Also, with the way the 7805 is setup on the BOE, with the heatsink,
can it handle 12vdc? Thanks, Chris
Also, with the way the 7805 is setup on the BOE, with the heatsink,
can it handle 12vdc? Thanks, Chris
Comments
CHRIS@R... writes:
> Can anyone tell me what the maximum current output of a 7805 is?
> Also, with the way the 7805 is setup on the BOE, with the heatsink,
> can it handle 12vdc? Thanks, Chris
>
Max output is 1 amp. Will handle 12 volts input quite comfortably.
Sid
[noparse][[/noparse]Non-text portions of this message have been removed]
Stamp is about 50ma.
A uA7805 TO-220 package with no heat sink is about 500ma, one with a good
heat sink can push 1.5 amps max.
http://www-s.ti.com/sc/psheets/slvs056g/slvs056g.pdf
The uA7805 in surface mount form (looks like a cutoff TO220) is typically
500ma to 1 amp, depending on the heat sink surface it is soldered to.
A LM123/LM323 TO-3 package typically can handle up to 3 amps with heat sink.
http://www.national.com/ds/LM/LM123.pdf
The 7805 can handle 12v in, but the little tiny 7805 on the Basic Stamp may
not like it so much,
I've had the on Stamp 5v Regulator run hot with 12v in before, changing the
Stamp to use the 5v output from the larger 7805 instead would not be a big
problem.
Original Message
From: christopher41877 [noparse]/noparse]mailto:[url=http://forums.parallaxinc.com/group/basicstamps/post?postID=wx3bB0Q9sducueBI0LwDDmfUmY3dIHQiWqhq5Y055w-YDKWpvvOhWWFf0dz9OqKYKy3iP_8cgy5QEHYzW0NniW1LgxOA]CHRIS@R...[/url
Sent: Saturday, June 29, 2002 8:05 AM
To: basicstamps@yahoogroups.com
Subject: [noparse][[/noparse]basicstamps] MAX OUTPUT OF 7805
Can anyone tell me what the maximum current output of a 7805 is?
Also, with the way the 7805 is setup on the BOE, with the heatsink,
can it handle 12vdc? Thanks, Chris
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Any 7805 will output 1 amp unless it has an "L" in it. i.e. 78L05. If this is
the case it will only output 100ma. If the current exceeds the rated value it
will go into short circuit protection and cut out. Any of the 78xx series can
accept approximately 1.2 to 27 volts on its input. Here is the problem with a
linear regulator:
Say you need 5 volts at 1amp and apply an input of 12 volts. The amount lost in
the regulator will be:
12volts - 5 volts = 7 volts
7 volts * 1 amp = 7 watts.
Therefore the regulator will have to drop 7 watts to provide you with 5 watts.
As long as your supply puts out more than 12watts and your 7805 is adequately
heat sunk it should be fine.
-=Randy Knutson
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Vin Max, according to the National Semiconductor data sheet, is 35V.
Maximum output current of these regulators is 1A.
With the BOE, I probably wouldn't feed it with more than 15V due to the size
of the heatsink.
Remember, that if you were to feed the 7805 with 35 volts, you'd have a
voltage drop over it of 30V. If you were driving 1 Amp, you'd be
dissipating 30 Watts through that heatsink, which looks too small to handle
that amount of heat.
cheers,
Ben, windy Wellington, New Zealand.
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> From: "christopher41877" <CHRIS@R...>
> Reply-To: basicstamps@yahoogroups.com
> Date: Sat, 29 Jun 2002 13:04:35 -0000
> To: basicstamps@yahoogroups.com
> Subject: [noparse][[/noparse]basicstamps] MAX OUTPUT OF 7805
>
> Can anyone tell me what the maximum current output of a 7805 is?
> Also, with the way the 7805 is setup on the BOE, with the heatsink,
> can it handle 12vdc? Thanks, Chris
>
>
> To UNSUBSCRIBE, just send mail to:
> basicstamps-unsubscribe@yahoogroups.com
> from the same email address that you subscribed. Text in the Subject and Body
> of the message will be ignored.
>
>
> Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/
>
>
got a 48v (in) to 12v (out)
regulator (an NTE 1936) feeding my 7805. Both get quite warm, so I'm wondering
if this is the way to go. What
about a voltage divider? Would 1/2 watt resistors do? Or am I barking up the
wrong tree?
Thanks
Michael Bratkowski
Los Angeles, CA