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Foldback current limiter circuit

  1. Nov 28, 2012 #1

    i want to design a foldback current limiter circuit whose max current limit is 3 Ampere and short circuit current limit is 1 Ampere. Also output voltage is 28 volts which is same as input voltage ... can anyone help me in this regard....

    Thanks in advance...
  2. jcsd
  3. Nov 28, 2012 #2


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    Staff: Mentor

    Welcome to the PF.

    It will be hard to design a current limiting circuit that has Vin and Vout the same. You would usually need to tolerate a few tenths of a volt across a current sensing resistor, and you will need a series pass transistor to serve as the cutoff element to lower the output current. How much voltage drop Vin-Vout can you tolerate?

    Also, can the short circuit current limit be less than 1A? Otherwise your pass transistor must dissipate 28W in current limit...
  4. Nov 29, 2012 #3

    Vout should not be less than 27.5 volts.. This is the maximum that i can tolerate when the circuit is behaving well. when it is in fold back condition obviously voltage drops. yup short circuit current can also be less than 1 Ampere there is no such limit but not more than 1 ampere..

    i have design my circuit according to the attachment. but when the fold back of current starts mosfets gets very hot and then current again starts increasing because of overheating.. i have used heat sinks but still cant solve the issue. i have used 3 mosfets in parallel to reduce current i can reach a limit of 1.5 ampere max..

    Attached Files:

  5. Nov 29, 2012 #4
    also see the attachment


    Attached Files:

  6. Nov 29, 2012 #5


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    Staff: Mentor

    Have you labelled the type numbers on those two transistors correctly, basitccp?
  7. Nov 29, 2012 #6
    sorry .. the part numbers are just replaced.
  8. Nov 29, 2012 #7
    mosfet part number is interchanged with the transistor part number...
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