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Programmable precision and low noise DC current source

Category: Hardware
Product Number: LT3080

Hello everybody,

I’m in need of a programmable, precise and low noise DC current source capable of sourcing up to 3A DC at 9V DC. For that I designed a current source made of 3 parallel LT3080 for rough tuning and one parallel LT3092 for fine tuning, to add the currents together at the output. For the Rset and Rout I use digital potentiometers and a 1 Ohm resistor with a tolerance of 1% or better and low temperature drift. In the datasheet of the LT3092 there is a sub chapter about quieting the noise and it says to put a Cset parallel to Rset and also reduce the output current noise by putting a high C between the output and GND. Is it possible to still maintain stability if I use big electrolyte capacitors (C=4700uF maybe even multiple 4700uF, all low ESR<50mOhm)? For my system cost or size is no concern. Have you done tests with big C values? Is stability more important than high C to GND because of the inherent regulation of the LT3080 and LT3092?

This is the setup I use for both LT3080 and LT3092.

The input voltage is sourced by a lab DC source.

Do you have other ideas or tips for me?

What would you recommend for a precise and low noise DC current source?

Thank you in advance!

Best regards,

Max

Parents
  • Thanks for the post. The image below shows how I would make a 0A to 3A, 0V to 9V current source.  I also attached the LTspice file.  Let me know if you would like help designing the current sink to pull 300uA out of the SET pins.  My best guess is that you will need the 22uF caps on OUT of the LT3041s and also caps from SET to GND.  Your stability depends on your load.  Some series resistance will help stabilize an inductive load more than anything. 

    sim ckt and results_1.png

    LT8610A LT3041_5.asc

      

  • Thank you for your response! I didnt know about the LT3041 and I looked it up and it turns out to be way better in every way compared to the LT3080. Can I also use the LT3041 like I do my LT3080 and LT3092 right now as a parallelable current source like in the following picture (plus Cset): R13 and L2 are my Load I need to put 0 to 3A DC current into.

    So I can use digital potentiometers to programm Rset (R12) to set the output current? Is the same equation for the output current (Iout = Irefence * Rset / Rout) of the LT3080 also true for the LT3041? I don't completely understand why I would need a current sink for the SET pins. Can you explain that in more detail please?

    A problem I have with my current setup currently is that for setting the output current I have a 1 Ohm resistor at the OUT pins of the regulators which get hot at higher currents and induce temperature drifts into my system. I need the 1 Ohm resistor because digital potentiometer of lower resistance are hard to get with 1% precision and 1024 tabs. 20kOhm is the lowest I could find. For the LT3080 I'm using 100kOhm Rset potentiometers and 1 Ohm Rout for a max Iout of 1A.

    Because of the higher reference current of the LT3041 of 100uA I would then need a digital potentiometer of lower resistance like 20kOhm and Rout of 2Ohm which would mean more potent temperature effects. I'm currently also working on cooling the resistors to counter the temperature effects.

    Whats you opinion on this?

    Thank you for your work and ideas!

    I'm looking forward to your response!

Reply
  • Thank you for your response! I didnt know about the LT3041 and I looked it up and it turns out to be way better in every way compared to the LT3080. Can I also use the LT3041 like I do my LT3080 and LT3092 right now as a parallelable current source like in the following picture (plus Cset): R13 and L2 are my Load I need to put 0 to 3A DC current into.

    So I can use digital potentiometers to programm Rset (R12) to set the output current? Is the same equation for the output current (Iout = Irefence * Rset / Rout) of the LT3080 also true for the LT3041? I don't completely understand why I would need a current sink for the SET pins. Can you explain that in more detail please?

    A problem I have with my current setup currently is that for setting the output current I have a 1 Ohm resistor at the OUT pins of the regulators which get hot at higher currents and induce temperature drifts into my system. I need the 1 Ohm resistor because digital potentiometer of lower resistance are hard to get with 1% precision and 1024 tabs. 20kOhm is the lowest I could find. For the LT3080 I'm using 100kOhm Rset potentiometers and 1 Ohm Rout for a max Iout of 1A.

    Because of the higher reference current of the LT3041 of 100uA I would then need a digital potentiometer of lower resistance like 20kOhm and Rout of 2Ohm which would mean more potent temperature effects. I'm currently also working on cooling the resistors to counter the temperature effects.

    Whats you opinion on this?

    Thank you for your work and ideas!

    I'm looking forward to your response!

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