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ULN2003A: ULN2003A as a linear analog current-sink device

Ryan May
Genius 13700 points
Part Number: ULN2003A
Other Parts Discussed in Thread: XTR111

Hello,

I am working on a project where I need to control a current passing through a loop and while I would like control it using a PWM signal I can not have the the loop experience any sort of PWM switching.

This got me thinking that if a part such as the ULN2003A was controlled in the linear region by supplying a filtered PWM signal from an RC filter I could control the current passing through the loop as a function on the beta of the Darlington pair.

Do you think this is possible for this device? The benefit is that I can control multiple channels in a single device that is very cost effective.

Thank you for your support.

  • 0
    Guru 244350 points

    The ULN transistors are meant to be saturated, so you have to look at the power dissipation.

    Furthermore, their amplification (β) is not exactly specified, and somewhat random. So how do you control the absolute current level without some sort of feedback? As far as I can see, if you need feedback, you cannot avoid using one opamp per channel (or something like the XTR111).

    But the ULN transistors/resistors/clamping diodes do not behave any different from discrete parts.

  • 0 in reply to Clemens Ladisch
    TI__Genius 13700 points

    Hello Clemens,

    Thanks for chiming in here.

    I am not looking for anything fine tuned just some rather coarse adjustment.

    I will dig into this more but what you said about the beta being somewhat random has me confused. I would think that on the same die that they would be well matched to one another and that device to device that they would be a marginal variation of maybe +-10% at most.

    As with many questions I think that this going to be solved with time and tinkering.