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Old 1st May 2006, 07:46 AM   #1
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Default lm317 better topology?

This diagram is floating around the internet, and I wondered about it's merits or downsides:

http://www.edn.com/archives/1994/051...h/10di6fg1.htm

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Old 1st May 2006, 08:12 AM   #2
AndrewT is offline AndrewT  Scotland
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Hi,
there is nothing wrong with the re-located pot. The circuit still works.

But there are a couple of points that need attention.
1. the maximum value of the pot should allow the minimum current to flow from the regulator.

2. the range of adjustment is quite limited, in an unthinking moment one might be tempted to change the pot value without realising they are infringing 1. above. This makes a low resistance value pot mandatory.

This alternative solution does not overcome either of the problems above but I think the pot plus resistor should be paralleled with a fourth resistor to control the voltage range from the regulator and keep the circuit working if the pot starts to become noisy or opencircuit. It also allows a higher value pot to be used. It acts as a trimmer for the main voltage divider action of the series resistors.
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