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'[EE]:Better regulator'
2002\09\03@142442 by Jim

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Hi

I have a lcd tv and a dvd player I want to run on a 12v battery.
Like from my van battery or a 12v gellcell.
The dvd runs on a 12v wall wart rated at 1a.
The lcd tv runs on 6v@ 1a.
I have built a simple circuit using a 7812 & 7805 and it works fine
the tv works good on the 5v and draws .7a But these regulators get so hot
they must be wasting alot of energy are there better regulators I could use
in this app? the gellcell's I have are rated 12v @ 5ah/20h And I don't think
it will last very long driving these loads.

Thanks for any input

James M

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2002\09\03@143658 by mike

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Take a look at the Nat. Semi Simple Switcher products - LM2574 etc.
These will be much more efficient.
On Mon, 2 Sep 2002 23:27:36 -0700, you wrote:

{Quote hidden}

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2002\09\03@144106 by Rick C.

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What you have will work but is inefficient, and will dissipate a lot of heat. If
you use a 7805 in a TO3 case and a large heatsink, you'd be better off when
running off the car battery. However, running from a gelcell, you are wasting
power. A SMPS would be your best bet. The Linear Tech
(http://www.linear-tech.com) website has a program that will allow you to enter
your specifications and will select the proper device. National also has a few
good devices too. Overheating can also be caused by the regulator(s)
oscillating. A 0.1uf cap across each 78xx will stabilize them.
Rick

Jim wrote:

{Quote hidden}

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2002\09\03@144757 by Code

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The LCD Tv should run fine off a standalone gel cell or lead-acid battery,
should the battery be shared with your vehicle, use a 12V LDO regulator for
protection, instead of a 7812 as the latter requires a larger overhead
voltage to function properly. Switching regulators might be your answer for
higher efficiency voltage regulation. National Semi manufactures quite a
number of it. TTYL

Tan Chun Chiek.



{Original Message removed}

2002\09\03@144800 by Giles Honeycutt

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James,
Remember the formulas.  If you are going to pull 0.7A at 5VDC  you will have
drop the other 7VDC
That is 7 X 0.7 = 4.9 Watts on your little regulator.  The only way around
this power usage is to step the voltage down.  A DC/DC converter will do it.
Other methods would be to build a DC to DC.
A better regulator will not help.

But you could put 2 LCD TVs in series and consume the same amount of power
while watching 2 screens!!

Good luck,
Giles

> Hi
>
> I have a lcd tv and a dvd player I want to run on a 12v battery.
> Like from my van battery or a 12v gellcell.
> The dvd runs on a 12v wall wart rated at 1a.
> The lcd tv runs on 6v@ 1a.
> I have built a simple circuit using a 7812 & 7805 and it works fine
> the tv works good on the 5v and draws .7a But these regulators get so hot
> they must be wasting alot of energy are there better regulators I could
use
> in this app? the gellcell's I have are rated 12v @ 5ah/20h And I don't
think
> it will last very long driving these loads.
>
> Thanks for any input
>
> James M
>

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2002\09\03@152832 by Pic Dude

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Funny you should mention this.  I'm in a similar situation
trying to get +5V and +/-12V for a PC.  For the +5V signal,
I'm wondering why I can't use 2 6V gel cells in series and
pull the voltage off only one for the 5V signal (using an
LDO).  I've been trying to find out what happens when
charging 2 unequally-charged batteries in series.

Cheers,
-Neil.



> {Original Message removed}

2002\09\03@162228 by Rick C.

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It will work for awhile but I wouldn't. Maybe if you disciplined yourself and
occasionally swapped the two, you could get away with it but if you forgot when
you swapped them, after a period of time you'd unbalance the capacities and
damage one of them (guess which one?).

Here's a cute little board.

It's a switcher rated for over 1 amp. Its output can be fixed from 2.5 volts to
9 volts with a change of only one resistor, and an input range from about 7
volts to 20 volts. Under my test circuit, with 6 volts out, I  loaded it with
1.2 amps, and with an input voltage of 13 volts, it draws about 500ma. With an
input of 7 volts it drew about 750ma and with a 16 volt input, drew about
300ma. The switcher chip and the inductor were "barely" warm to the touch. I
came across about a dozen of these boards. I sawed them off a production board
from a run of video monitor cards in a notebook type computer for police cars.

http://www.pic101.com/pix/P9030001a.JPG

The unit is quiet too! I had an AM radio sitting next to it and heard no noise
or squeal until it dropped out of regulation below 6 volts input. I would like
to lay out a new board for them for a bunch of projects I'm working on and also
make them available to anyone on the list if interested in them. Contact me off
list if you're interested.
Rick

Pic Dude wrote:

> Funny you should mention this.  I'm in a similar situation
> trying to get +5V and +/-12V for a PC.  For the +5V signal,
> I'm wondering why I can't use 2 6V gel cells in series and
> pull the voltage off only one for the 5V signal (using an
> LDO).  I've been trying to find out what happens when
> charging 2 unequally-charged batteries in series.
>
> Cheers,
> -Neil.
>
> > {Original Message removed}

2002\09\04@050337 by o-8859-1?Q?Tony_K=FCbek?=

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Hi,

Rick C. wrote:

<snip>
>I would like
>to lay out a new board for them for a bunch of projects I'm working on
and also
>make them available to anyone on the list if interested in them.
Contact me off
>list if you're interested.
>Rick

Well this isn't off-list but I assume several people would be interested
in this type of thing so please post whatever you're willing to share on
the list.


/T

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2002\09\04@084903 by Rick C.

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I will post a notice and a link to the project (such as the one I did last
week) as interest in it picks up and I complete the documentation similar to
this one:  http://www.pic101.com/foxhound
Rick

Tony Kübek wrote:

{Quote hidden}

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2002\09\04@210952 by M. Adam Davis

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This wouldn't work well for a number of reasons.  Firstly the currents
for each would rarely be the same, and even if they were close enough
one would have a ground 5volts above the 'real' ground.  You'd have to
float the VCR or tuner feeding the second display, unless you want to
short out the 6volt supply through a ground.

-Adam

Giles Honeycutt wrote:

>But you could put 2 LCD TVs in series and consume the same amount of power
>while watching 2 screens!!
>
>Good luck,
>Giles
>
>

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