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Thread: How does this overpower/short circuit protection circuit works?

  1. #11
    diysmps Senior Member Silvio's Avatar
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    Apr 2015
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    Your lowest current adjustment will be 100mA or 0.1 amp you cannot go to zero

    Well 100ma that variation is nothing compared to the full range. You must have a 10watt resistor of 0.06 ohms otherwise you can opt for 2 X 0.1 ohm by 5watt resistors in parallel but this gives a different value and the range will step up to say 12 or 13 amp. To cure that you must change the resistors for the 0.6v reference and make them to get 0.5v reference instead. Do not forget that the lower the value of the sense resistor the resolution for the current sense will worsen. If for example you opt for a 0.1 ohm then your reference has to be 1v. This will give better resolution and current sense will be more accurate. Yet again you then have more dissipation in the sense resistor and because of that you have to make a larger wattage resistor.

    The wattage in the resistor is calculated by ohms law hence 10 amps X 0.06 ohms = 0.6volts then power of resistor will be 0.6volts X 10amps which will give a power of 6 watts hence a 10watt resistor will be suitable.

    If for example we opt for 1volt reference and a sense resistor of 0,1 ohm is chosen then the power dissipation in the resistor will be 1v X 10 amps =10 watts yet again a 20 watt resistor must be chosen other wise it will heat up and change value.

    A compromise have to be set according to your need either the lower value but not so accurate or the higher value will be more accurate but need a larger watt sense resistor.

    One last comment I suggest you use a 10 turn pot for adjustment of voltage and current

    Hope that helps
    Last edited by Silvio; 07-14-2017 at 11:24 PM.

  2. #12
    Many THANKS silivio for the hints.
    My sense resistor is a homemade one with a piece of wire from a 2 Ohms 10W wound resistor.

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