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Old 24th March 2009, 04:16 PM   #1
kirtm is offline kirtm  United States
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Default monitor voltage input

I have been tasked to design a piece of test equipment to test an Lm338 circuit used as a current limiter. I would like to monitor (LED?) a variable input supply (+4 to +20VDC) (2.0A) through a switch that would supply the LM338 circuit. Something that would show that power was supplied to the circuit. Any suggestions? Thanks.
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Old 10th April 2009, 04:28 PM   #2
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Default c here
Wrap it in foil, and plug it in.
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Old 10th April 2009, 05:55 PM   #3
AndrewT is offline AndrewT  Scotland
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Location: Scottish Borders
a LED with a couple of series diodes and a resistor (3k) will do that.
The 1.6V LED (red) + 1.4V (two diodes) will be off @ <=3V.
At maximum voltage it will be very bright. At minimum voltage it will be very dim.

You could replace the two diodes with a two terminal CCS. Buy a 5mA CCS it will show constant brightness >=6V and dim as 4V approaches.
regards Andrew T.
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