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Variable Current Limit with Steady Voltage

ag273n

Nov 24, 2016
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several months ago, i created my variable power supply using an LM317 - it was working great and I have been using just about on every electronics experiment I do... but that PSU can only output 1.5A max and cannot limit the current output.

now i have the LM338 - which can do 7A max, and i want it to include a way to limit the current output (variable) with a steady output.
so how do you make a variable limit to the current draw - with the same voltage?

upload_2017-2-28_16-10-45.png
the above diagram is what i'm hoping to build...
i tried looking up online for any tutorials, but i could hardly find one thats worth reading...
 

Audioguru

Sep 24, 2016
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When you limit the current then the voltage drops according to Ohm's Law.
A second LM338 can be used as a current limiter ahead of the voltage regulator. A current limiter and a current regulator are shown on the datasheet of the LM338.
 

ag273n

Nov 24, 2016
74
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Nov 24, 2016
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i found this from the datasheet:

upload_2017-3-1_10-34-18.png

so i'm guessing just connect this in series to the earlier schematic i have... correct?
 

Audioguru

Sep 24, 2016
3,656
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i found this from the datasheet:

View attachment 32360

so i'm guessing just connect this in series to the earlier schematic i have... correct?
Of course. Probably ahead if the voltage regulator.
This current limiter has a voltage drop so the input voltage must add it to the voltage regulator input requirement.
 
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