16vdc@6.5Amps down to 12vdc@4.5Amps

[Jack Snodgrass]

I have a DC supply that says 16vdc@6.5Amps out...

I have a DC Device that wants 12vdc@4.5Amps in....

I know ( think ) that I can use a LM7812 to step down
the volts from 16 to 12... but the LM7812 is only rated
to 1Amp.

Also... a LM7812 says that the output varies from 11.5 - 12.5
(min 11.5, typical 12.0, max 12.5 ). I want 12.0 +- 0.2 ...
not 12.0 +- 0.5.

How is this normally handled?

Thanks - jack

 

[Brian]

Jack Snodgrass wrote:

I have a DC supply that says 16vdc@6.5Amps out...

I have a DC Device that wants 12vdc@4.5Amps in....

I know ( think ) that I can use a LM7812 to step down
the volts from 16 to 12... but the LM7812 is only rated
to 1Amp.

Also... a LM7812 says that the output varies from 11.5 - 12.5
(min 11.5, typical 12.0, max 12.5 ). I want 12.0 +- 0.2 ...
not 12.0 +- 0.5.

How is this normally handled?

Thanks - jack

Jack,

The simplest solution would be to use a LM338K regulator. If you want to
use the LM7812, you would need to use a power transistor to boost the
current, up to the 4.5 amps that you want. To do that, I drew up the
schematic for you. You can see it at http://www.fncwired.com/12VoltEx/

If you would like to go the switching regulator route, I could draw up
the schematic for that too. Let me know.

Brian


--
Building user friendly software for electronics.
http://www.fncwired.com

 

[Keith R. Williams]

In article <pan.2003.12.31.16.39.10.563997@mylinuxguy.com>,
jack+ntlug@mylinuxguy.com says...

I have a DC supply that says 16vdc@6.5Amps out...

I have a DC Device that wants 12vdc@4.5Amps in....

I know ( think ) that I can use a LM7812 to step down
the volts from 16 to 12... but the LM7812 is only rated
to 1Amp.

Also... a LM7812 says that the output varies from 11.5 - 12.5
(min 11.5, typical 12.0, max 12.5 ). I want 12.0 +- 0.2 ...
not 12.0 +- 0.5.

How is this normally handled?

A better regulator? ;-) Seriously, 4V @ 4.5A is 18W, which is quite a
bit of heat to dissipate, but not an impossible task. I'd look around
for a buck regulator design to try to reduce the waste heat. Buck
regulators will be more complicated than a linear, but will simplify
your cooling.

National (http://www.national.com) has some pretty good application
notes on line. I've "stolen" buck regulator designs from their app
notes a time or two. ;-)

--
Keith

 

[Garrett Mace]

National (http://www.national.com) has some pretty good application
notes on line. I've "stolen" buck regulator designs from their app
notes a time or two. ;-)

--
Keith

Hmmm, I think "adapted" works well as a word choice in those situations.

 

[Rheilly Phoull]

"Garrett Mace" <g.ryan@macetech.com> wrote in message
news:mHEIb.196769$Eq1.22383@twister.rdc-kc.rr.com...

National (http://www.national.com) has some pretty good application
notes on line. I've "stolen" buck regulator designs from their app
notes a time or two. ;-)

--
Keith


Hmmm, I think "adapted" works well as a word choice in those situations.

Nahhh !! I like the brutal honesty
(So refreshing in todays values)
--
Regards ............... Rheilly Phoull

 

[Keith R. Williams]

In article <3ff4b329$0$1736$5a62ac22@freenews.iinet.net.au>,
shredder@bigpong.net says...

"Garrett Mace" <g.ryan@macetech.com> wrote in message
news:mHEIb.196769$Eq1.22383@twister.rdc-kc.rr.com...
National (http://www.national.com) has some pretty good application
notes on line. I've "stolen" buck regulator designs from their app
notes a time or two. ;-)

--
Keith


Hmmm, I think "adapted" works well as a word choice in those situations.



Nahhh !! I like the brutal honesty
(So refreshing in todays values)

The unvarnished truth is that I'm not paid to produce a result,
not to invent. Well, I am paid to invent, but certainly not to
(re)invent buck regulators. I'm not above stealing other's
designs (patent issues excepted) to get my work done. Though I
am nice enough to buy their parts. ;-)

--
Keith