telford dorr
Samba Member
Joined: March 11, 2009
Photos: 225
Location: San Diego (Encinitas)
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| Constant Current Source Circuit |
Posted: Sun Oct 26, 2014 4:20 pm Views: 131
Rating: Not rated
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This circuit is useful for measuring low ohms resistances. It will put a constant 100 ma current into an unknown resistance. By measuring the voltage across the unknown resistance, you can determine its value.
A regular DMM can't do this accurately because its test lead resistance and connections become significant when measuring low resistances. This circuit eliminates this problem.
For example, suppose you measure 0.125 volts across an unknown resistance. Its value is 10 times this number, or 1.25 ohms. [R = E / I = E / 0.1]
The circuit needs a minimum of 3.0 volts from 'power +' to 'load +' to regulate properly. See a LM317T datasheet for details. |
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