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Thread: capacitor value?

  1. #1

    Default capacitor value?

    i'm using Diodes Inc. driver chip AL8861 to drive 2 LEDs per string.
    they recommend 4.7 to 10uF cap.
    "The minimum capacitance needed is determined by input power, cable‘s length and peak current. 4.7μF to 10μF is a commonly used value for most cases. A higher value will improve performance at lower input voltages, especially when the source impedance is high."

    my input voltage can be as low as 10 volts. LEDs are no more than 2" away from driver. peak current is 1amp.
    i've been using 10uF caps but they have greatly increased in price.

    when they say "improve performance", does that mean running at lower required current?
    can i safely use 4.7uF caps?

    thanks

  2. #2

    Default Re: capacitor value?

    Quote Originally Posted by mercrazy View Post
    i'm using Diodes Inc. driver chip AL8861 to drive 2 LEDs per string.
    they recommend 4.7 to 10uF cap.
    "The minimum capacitance needed is determined by input power, cable‘s length and peak current. 4.7μF to 10μF is a commonly used value for most cases. A higher value will improve performance at lower input voltages, especially when the source impedance is high."

    my input voltage can be as low as 10 volts. LEDs are no more than 2" away from driver. peak current is 1amp.
    i've been using 10uF caps but they have greatly increased in price.

    when they say "improve performance", does that mean running at lower required current?
    can i safely use 4.7uF caps?

    thanks
    - What is your power source?
    - What are you making?

    You could possibly run with much smaller caps and be fine if you don't care about current accuracy, response time to Vset changes, etc. .... or EMI. You do at some level need to be concerned about ripple current too.

  3. #3

    Default Re: capacitor value?

    car/boat battery with alternator or stator charging.
    portable light.

    exact current is not critical but don't want noticeable change in brightness.

  4. #4

    Default Re: capacitor value?

    Quote Originally Posted by mercrazy View Post
    car/boat battery with alternator or stator charging.
    portable light.

    exact current is not critical but don't want noticeable change in brightness.
    If the 4.7uF are less than 1/2 the cost of the 10uF you could use 2 of them. I believe capacitors in parallel ADD values together.
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