Re:[AVR-Chat] Powering an AVR with a switching regulator
2008-09-17 by xolang1
Hi Have you considered AC first then transform this to DC at the far end? --- On Wed, 9/17/08, Tim Mitchell <tim@sabretechnology.co.uk> wrote:
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From: Tim Mitchell <tim@sabretechnology.co.uk>
Subject: RE: [AVR-Chat] Powering an AVR with a switching regulator
To: AVR-Chat@yahoogroups.com
Date: Wednesday, September 17, 2008, 4:12 PM
Chuck Hackett wrote:
> My railroad signal application will require powering the boards over
> a long distance (> 1,000 feet) from a head-end power supply. To
> overcome problems with the voltage drop along the cable run I am
> looking at using a switching regulator to cut the possible 24-36vdc
> power bus (falling to maybe 10-12 v at the far end) down to the 5v
> required on the board.
>
> I am looking into switching regulators because they are more
> efficient at dropping higher voltages down to 5v levels. I expect a
> current draw of 100ma on up to a possible max of 700ma.
>
> One example would be the LT-1076-5
>
(http://www.linear. com/pc/productDe tail.jsp? navId=H0, C1,C1003, C1042,P198
3)
>
> My concern is the noise generated by the regulator's switching
> activity.
>
> Assuming I use a circuit suggested by the manufacturer, keep traces
> short, and keep the regulator circuit away from input lines am I
> likely to run into problems with noise causing the AVR to operate
> erratically?
>
> My board does not involve sensitive A/D inputs. The only A/D input
> is a low-impedance, slow changing signal that goes through a low pass
> filter before it gets to the AVR.
>
> I had thought of powering an intermediate internal power bus from the
> switcher and then using a linear regulator down to 5v but I'd rather
> avoid the extra real-estate and cost.
>
We have done a lot of AVR stuff powered with National Semi's "simple
switchers" with no problems, they usually just work like a 7805 but a
lot less heat!!. They have a design tool called Webench on their website
to tell you the right components to use around the switcher for trouble
free operation.
E.g. LM2592HVT-5. 0 will give you a nice efficient 5V @ 2A from up to 60V
input. It's a TO-220/5 package so easy to make prototypes with.
--
Tim Mitchell