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Is it possible to make a constant DAC controlled current source using LT3092

Category: Hardware
Product Number: LT3092

I am trying to make a constant current source using LT3092 .My DAC maximum output is 3.3V and at that time the current source needs to generate a current of 20mA.

For generating 20mA the RSET(R1 in schematic) value needs to be 165 Ohm . Please see my circuit below.

The issue what I am facing is my load will come in series with RSET and this is changing the desired current. May I know is there any way to solve this issue.

Below is the circuit with load.You can see that the current is changed.

I want my output current to be independent of load .Can you please help me

Parents Reply
  • Hi ,

    I few points to keep in mind when doing adjustable current source design based on the circuit shown above:

    • The SET pin should not be left floating in any case. Will cause maximum current to flow to the load. Especially make sure that the pin is not floating during power up (in the proposed circuit, place, say, 1k resistor from SET to ground. That will help in keeping the Iout small while the opamp is "waking up").
    • When the DAC is powered up, its output may, depending on the chosen chip, default to high impedance or e.g. mid-voltage value. Choose DAC that wakes up to zero output and/or place a,say, 1k resistor from DACs output to ground. if the DACs output is floating, the summing amplifier may "run-away" due to net positive feedback if the load impedance is greater that the shunt resistor Rshunt.

    Measure the current output at power up. A current spike may damage your load.

    Cheers, heke

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