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  1. #1
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    High Precision Programmable Current LED Driver

    Hello All,

    I need to design current stabilized LED drivers. (Requiring very low noise, low thermal drift of LED currents)

    Main supply voltage is 15V dc

    LED currents are about 500mA each. I also need to adjust the LED currents btw 200 .. 600mA individually for each channel. I can use DAC outputs (0..3.3V) or adjustable pots for this.

    I thought I can use an Opamp and Transistor and a feedback resistor but there is too much voltage drops at the transistor and transistor becomes hot.

    If there are application specific ICs for this it is the best for me.

    Any opinions, recommendations, part numbers will be appreciated.


    PS. There will be 4 different channels on the same board and only one LED will be turned on at a time.
    Best Regards

    Sobakava

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  2. #2
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    Re: High Precision Programmable Current LED Driver

    Any already-designed audio power amplifier that has low noise and low thermal drift should work, if you removed the AC-coupling caps, if any, and used it to push DC current.

    Have you looked at the "chip amps" that are available, such as LM1875 (and maybe LM675). And there are many, many more. Not sure if they will all work with such a low supply voltage. But definitely there are some that will. They make it extremely simple to implement a power amplifier.



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  3. #3
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    Re: High Precision Programmable Current LED Driver

    The op amp and transistor circuit is fine but you have a lot of power to dissipate if you are operating the LEDs from a 15V supply (in the neighborhood of 6W at 500mA). You can add a power resistor in series with the LED to dissipate some of the power (for example an 18Ω, 10W resistor will drop 9V and dissipate 4.5W at 500ma). Also you will likely need to heat sink the transistor.
    Zapper
    Curmudgeon Elektroniker



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  4. #4
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    Re: High Precision Programmable Current LED Driver

    Many voltage regulators can be used to regulate current. See http://www.ti.com/lit/ds/symlink/lm340-n.pdf for an example.

    Do you need it to be programmable? You say you can use a pot which conflicts with the title.

    Do you wish to use PWM? To lower the power dissipation, or/and a means of controlling brightness?



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