Powering an AVR with a switching regulator
2008-09-17 by Chuck Hackett
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,P1983) 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 Id rather avoid the extra real-estate and cost. Thoughts? Cheers, Chuck Hackett "Good judgment comes from experience, experience comes from bad judgment" 7.5" gauge Union Pacific Northern (4-8-4) 844 http://www.whitetrout.net/Chuck