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Thread: 1000w smps based on LUDO3232

  1. #361
    .... Silvio's Avatar
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    Upik here is a diagram to help you understand better

    probe.JPG

  2. #362
    diysmps Senior Member
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    yes I understand now, for the primer on my smps to reach 350v, if to divide a smaller voltage, for example 150v, does the dividing resistor have to be adjusted too?
    with the scope specifications I have, with a max input of 40v peak, is it safe for Silvio, ??
    Last edited by Upik; 12-01-2018 at 07:43 AM.

  3. #363
    .... Silvio's Avatar
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    The resistive divider will also work for lower voltage of 150v. it will divide by 10 and the voltage at the probe will be 15v.

    Note During test do not touch laptop or scope. Be careful !!!
    Last edited by Silvio; 12-02-2018 at 08:05 AM.

  4. #364
    diysmps Senior Member
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    what if using a 2x47k (2 watts) 10k (2watt), is that not a problem in reading

  5. #365
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    Quote Originally Posted by Upik View Post
    what if using a 2x47k (2 watts) 10k (2watt), is that not a problem in reading
    The wattage in the resistors is there so that they do not burn with the voltage applied to them. If you have larger watt resistors its no problem.

    This is how I worked it. There is around 350v volts at the primary so first we work out the current with ohms law

    V= I x R so V/R =I so 350v / 100000 ohms = 0.0035A or 3.5mA

    W = V x I so 350v x 0.0035A = 1.225W

    You have to choose a larger watt resistor than 1.2W because it will heat up a lot however I divided the resistor of 100k with 2 x 47k so that the power will be divided. However most of the voltage drop will be in the 47K resistors. The 10K resistor will not have a lot of voltage drop in it so 1watt will be enough.

    I hope that helps.

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