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[aprssig] EMI Help (fixed)

Andrew Rich vk4tec at hotmail.com
Fri Aug 13 05:31:38 UTC 2004


Regulator is to hot to touch

It is having troubles loosing 14 volts down to 5 volts

I am going to switch mode

Cheers

PS 5 volts at 170ma Thats LCD light on, GPS and PIC and MAX232

----- Original Message -----
From: "Scott Miller" <scott at 3xf.com>
To: "'Andrew Rich'" <vk4tec at hotmail.com>; "'TAPR APRS Mailing List'"
<aprssig at lists.tapr.org>
Sent: Friday, August 13, 2004 3:10 PM
Subject: RE: [aprssig] EMI Help (fixed)


What are your power requirements?  Linear regulators are going to dissipate
a fair amount of power in the process of bringing the voltage down.  You
probably want something like a buck converter.  The MAX5035 is an automotive
step-down converter that'll give you 1 amp at 5 volts from up to 76 volts at
up to 94% efficiency.  It's a little more involved to implement than a
linear regulator, though, and requires an external inductor to do its job.
That's just an example - I found that on Maxim's parametric search, and you
might have trouble actually getting that part in less than huge quantities.
There are plenty of others like it, though.

I run OpenTrackers off 13 volts all the time with 78L05 regulators and I've
got no overheating problems.  Average draw is maybe 10 ma.  Is your
regulator really getting hot, or could something else be thermally
sensitive?

Scott
N1VG

-----Original Message-----
From: aprssig-bounces at lists.tapr.org
[mailto:aprssig-bounces at lists.tapr.org]On Behalf Of Andrew Rich
Sent: Thursday, August 12, 2004 9:51 PM
To: Andrew Rich; TAPR APRS Special Interest Group
Subject: Re: [aprssig] EMI Help (fixed)


Thanks to all that helped. Here is what I did :-

1. Shortened the LCD data bus lead by half
2. Changed the code so there are less interrupts (less chance of glitches)
3. Added a 0.1uF across the Vin and Vout (I already had 10uF on Vin and V
out)
4. Added a 0.1uF across the GPS in data line
5. Wound the input voltage leads in a ferrite bead.
6. Moved the caps closer to the voltage regulator

Now I am up against thermal stress. I turned up the heater in the car and
the regulator started to give up.
Bring the temperature back again and all is well.

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 ?

Cheers Andy VK4TEC






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