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LM234: Constant current source temperature dependence query

Amal Sivaji
Prodigy 60 points
Part Number: LM234


Tool/software:

Hi, 

     We would like to use LM234 programable constant current source IC in one of our circuits. I want to use the IC as a constant current source with 16uA in a temperature range of 10 to 40 deg C. I would like to know whether the current value (16uA) will change with respect to temperature in 10 to 40 deg C with a fixed Rset resistor of 4.2K 1% tolerance. 

  • 0
    TI__Expert 4520 points

    Hi Amal,

    Thanks for your question!

    Below is a screenshot showing the relationship between voltage across Rset and temperature as well as the schematic for a basic curent source:

    Since the voltage across Rset changes with temperature, the resulting current I_R will also change, so I_set is affected by temperature.

    I hope this helps!

    Best Regards,

    Andrew Li

  • 0 in reply to Andrew Li
    Prodigy 60 points

    Hi,

          I have used LM234 as a zero-temperature coefficient current source. I used 8.35K as my R1 resistor and 83.5K as my R2 resistor and used the diode 1N457. as per the formula given in the data sheet, my Iset should be 16.04uA, but practically I am getting 14.3uA and the Iset is increasing with temperature. I have tried to use 91.85K as R2 also. still, I am not able to get 16uA current and 0 temperature coefficient. Could you help me solve this out. I used the formula Iset= 0.134/R1 and R2=10R1

  • 0 in reply to Amal Sivaji
    TI__Expert 4520 points

    Hi Amal,

    Thanks for the update!

    Do you have anymore information about the situation you are seeing? When you see 14.3uA, how much is Iset increasing with temperature?

    Also, what are the tolerances of the resistors you are using as well as the input voltage Vin?

    Best Regards,

    Andrew Li