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Voltage or PWM controlled resitor

Discussion in 'Electronic Design' started by Teten, May 21, 2007.

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  1. Teten

    Teten Guest


    How can I realize a voltage or PWM controlled resistor to change
    current into a LED based system ?

    Current = 10mA to 350mA

    DC voltage controlled resirtor or PWM (duty cycle) controlled resitor

    Thank you a lot for your help.

    Best regards,
  2. Mook Johnson

    Mook Johnson Guest

    A current mode PWM controller will effectively drive the LED with a current
    instead of a voltage. Play some games with the voltage refereance and you
    should be able to get the range of currents you seek.
  3. Winfield

    Winfield Guest

    I'll see if I can answer your question. First, voltage-controlled
    current source circuits are often considered, and are a good way to
    make programmable currents. A simple current source can be created
    if the load is floating, rather than grounded.

    A true or "pure" current source, "sources" current into a grounded
    load, and this needs a power current mirror as part of its design.
    ASCII circuit diagrams for both of these have been posted here on
    s.e.d. multiple times, and are available with a Goggle search.

    Finally, let's address your question about a PWM resistor. While
    I wouldn't use a PWM resistor, per se, for your LED-current source,
    a PWM programming-signal makes plenty of sense. This can be used to
    create a PWM current (full on or off with a PWM ratio) into the
    mentioned above, and if the mirror has a smoothing filter capacitor,
    then the PWM signal will create a steady programmable current out of
    the mirror into the LEDs.
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