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  1. #1
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    Input and output capacitors for AMC7135

    Hi!

    The datasheet for the AMC7135 linear regulator shows that it needs input and output capacitors:

    http://www.addmtek.com/products/pdf/DD031-AMC7135_D.pdf

    The cheap drivers from DealExtreme do not have those capacitors. This causes problems if you have longer wires. Apparently there is voltage surge when you turn on or off the light. After burning down two voltage controllers I added the capacitors and it cured the problem.

    Now, I have a question: if I pool the AMC7135 chips - like 8 in parallel to achieve 2.8A for XM-L, do I also need to increase the capacitors? I.e. instead of 1uF input capacitor use 8uF input capacitor and instead of 0.1uF output capacitor use 0.8uF output capacitor?

    Arne

  2. #2
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    Quote Originally Posted by arnea
    Hi!

    The datasheet for the AMC7135 linear regulator shows that it needs input and output capacitors:

    http://www.addmtek.com/products/pdf/DD031-AMC7135_D.pdf

    The cheap drivers from DealExtreme do not have those capacitors. This causes problems if you have longer wires. Apparently there is voltage surge when you turn on or off the light. After burning down two voltage controllers I added the capacitors and it cured the problem.

    Now, I have a question: if I pool the AMC7135 chips - like 8 in parallel to achieve 2.8A for XM-L, do I also need to increase the capacitors? I.e. instead of 1uF input capacitor use 8uF input capacitor and instead of 0.1uF output capacitor use 0.8uF output capacitor?

    Arne
    Probably not. The important thing is a low impedance path between the 7135 and the capacitors. The longer the wire or circuit board trace is between the two the less effective the capacitor will be. Therefore you might need more than one capacitor, but I doubt that you will need eight.

  3. #3
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    I.e. instead of 1uF input capacitor use 8uF input capacitor and instead of 0.1uF output capacitor use 0.8uF output capacitor?
    My Guess is that this is correct, 8x the values, not 8x Capacitors. I am trying to keep my wires as short as possible to stay on the safe side and I use multiplies of the values @ the input only, as output wire is usually shorter than 3cm AND input V+ is around 10.

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