how to add overload circuit to my circuit

Discussion in 'The Projects Forum' started by new_eng, Oct 20, 2011.

  1. new_eng

    Thread Starter New Member

    Oct 20, 2011
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    [​IMG][​IMG]



    hii i build this nice circuit and i change mosfet to another mosfet irf460 to drive motor 220v DC 7 Amp and for sure i add power supply

    but i need to add over load circuit what suggestion circuit and how i connect it to my circuit , how to change or adjust it to disconnect for 5 amp or 7 amp for example and disconnect if a short happen
    thank you
     
  2. #12

    Expert

    Nov 30, 2010
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    8,183
    Have you thought of installing a fuse?
     
  3. new_eng

    Thread Starter New Member

    Oct 20, 2011
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    yas sure there is a fuse
    but i need circuit better
    you can't depend 100% to fuse
    i saw befor circuit damage (full damge ) and and fuse is still working ?!?
    i think i best safety include
    - over load circuit
    - circuit breaker
    - fuse
    -and other

    so i need over load circuit to learn ,safety and tell me how to adjust it to disconnect by different Amb WITH NICE CIRCUIT
    thank you
     
  4. Longhair

    New Member

    Dec 5, 2010
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    Maybe a couple fuses with different values in the circuit would be an option.
     
  5. crutschow

    Expert

    Mar 14, 2008
    14,846
    3,828
    The problem is that the semiconductor is faster than the (mechanical) fuse. You might Google "electronic fuse" for some ideas.
     
  6. praondevou

    AAC Fanatic!

    Jul 9, 2011
    2,939
    489


    In your circuit a short is different from an overload. If you short L+ and L- there will be nothing to limit the current through the Mosfets apart from the wires/ leads impedance and the RdsON. Mosfets have quite a high pulsed drain current rating , if you use two IRF460 that's more than 150A. A fast acting fuse of 10A at the input will possibly blow before your MOSFET does.
    With a circuit measuring the source current and then acting directly on the gate driver or after it you will have a better chance I guess. You could join the two sources of the Mosfets, put a current measuring resistor in series, pass the measured voltage through a comparator and to avoid changing your original circuit drive the Mosfets with a let's say IR2110 (the low side) and use the comparators output signal to shutdown the IR2110....something like this...

    You can also measure the current with a Hall sensor like THIS one. $4.50 at Digikey. It doesn't introduce much resistance like in the example above and can also be easily adapted to the shutdown input of the IR2110 or act directly on your circuits driver circuit.
     
    Last edited: Oct 20, 2011
  7. new_eng

    Thread Starter New Member

    Oct 20, 2011
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    is any circuit please

    thank you
     
  8. praondevou

    AAC Fanatic!

    Jul 9, 2011
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    489
    Looks confusing, I know.
    It won't work down to 8V because of the undervoltage protection of the 2110. If this is important , this chip can't be used in your case.

    You need to add a regulator or zener for the 5V supply of the hall sensor.
    You can adjust the limit with the pot at the non-inverting input of the comparator. I didn't draw the supply for the LM2903. Should be fast enough to protect your mosfets from overload.
     
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