AVR-Chat

On 17 Sep 2008 at 9:12, Tim Mitchell wrote:

> 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/productDetail.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
> 
> 
> ------------------------------------
> 

	I have used this design: 
	
	Ultra Simple 5V Switchmode Regulator
	http://sound.westhost.com/appnotes/an006.htm

	A nice cheap switching regulator.

	There is an even better version here:

	Simple Switching Regulator
	http://www.techlib.com/electronics/regulators.html

	Mark Jordan