[OZAPRS] Re: EMI Help (fixed)

[Andrew Rich]

thanks Hamish.

I added a heatsink, and all is well ;-)

have all the bits for a switch mode as well.

the LCD backlight was chewing up all the power 

----- Original Message ----- 
From: "Hamish Moffatt" <hamish at cloud.net.au>
To: <ozaprs at marconi.ics.mq.edu.au>
Sent: Sunday, August 15, 2004 2:01 PM
Subject: Re: [OZAPRS] Re: EMI Help (fixed)


On Fri, Aug 13, 2004 at 02:50:08PM +1000, Andrew Rich wrote:
> What is the best way to get from car volts (14Volts) down to something
> acceptable for a 5 volt regulator ?
> Most of the problem from running off the car is heat dissapation.
Getting
> from 14Volts down to 7ish volts.
> Voltage divider ?

Voltager divider won't help; you'll be dissipating the same amount of
heat either way. You need the regulation too.

Guess you are using a 7805 in the TO-220 package. It's good for 1 amp in
that package, but at 7V drop times 1 amp, it's dissipating 7W. In short
it needs a heatsink!

Unless you can improve your efficiency, then all solutions mean using a
heatsink, and possibly a fan (probably not needed). There are other
devices available in other packages which are easier to bond to big
heatsinks, like a TO-3 package. There's such a thing as an 7805K (TO-3)
but you probably won't be able to find one. Instead consider an LM317K.
The 317 is an adjustable regulator (unlike the 78xx family) and needs
some resistors to set its output voltage.

The only way to improve efficiency would be a switchmode solution. There
are devices in a TO-220-like package that are switchmode, but I don't
know anything more about them.

Hamish
-- 
Hamish Moffatt VK3SB <hamish at debian.org> <hamish at cloud.net.au>
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