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    Shortcircuit protection circuit

    Hi,
    I need a fast and simple short-circuit(or Over-voltage) protection circuit. My input voltage is 24V and max output current is 2A. How can I protect my power supply from over-current?
    I need the simplest and reliable circuit.

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    Re: Shortcircuit protection circuit

    Hi,

    I need a fast and simple short-circuit(or Over-voltage) protection circuit.
    "short circuit" is completele different to "over voltage" protection. it makes no sense to choose one OR the other.

    How can I protect my power supply from over-current?
    Well, then tell us how you decide it to work.
    there are a lot of possible solutions: Switch OFF when current gets higher than 2.00A - even for a short time like 1us. Automatic retry or not. Allowed overcurrent for x Amperes for x time (maybe to charge a capacitor), just limit the current to 2.00A...and many more.

    I need the simplest and reliable circuit.
    Simple, cheap and reliable:
    Use a fuse.

    Klaus
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    Re: Shortcircuit protection circuit

    Thanks Klaus for your points.
    Yes I know, for my circuit I need a short-circuit protection circuit. It should power off the output if short circuit happens automatically.( for example the current goes more than 2A)(Because I said such as over-current circuit). Output voltage and current are 24V and 2A(max) respectively.
    But fuse will burn by a over-current and you should dissemble your box to repair it.



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    Re: Shortcircuit protection circuit

    Hi,

    But fuse will burn by a over-current and you should dissemble your box to repair it.
    From the information you gave until now: itīs the same with the new circuit.
    You just describe that it should shut OFF (like a fuse) but you did not describe how/when it should be ON again. Thus I assume you want it to be OFF infinitely.

    You want it to be act as a fuse. But every fuse has a current-to-trip-time specification. Yourīs does not.
    Nor do we know what supply you want to use and what load you want to use.

    Thus my (simple and reliable) recommendation:
    Use a fuse with fuse holder mounted in the case, so that the fuse can be replaced without disassembling the box.

    Klaus
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    Re: Shortcircuit protection circuit

    Thank you again for your comment.

    As the Short circuit happens it should turn it off and be powered-off until the short-circuit be removed and after it turns the output on.



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    Re: Shortcircuit protection circuit

    So you have a 24V supply and you want to protect its output from short circuits?

    The good news is that there are many IC's that will do this by acting like a 'smart fuse'. You want to search 'load switch'. Here are a couple examples:
    -FPF2700
    -ISP762T

    But there are lots of choices, high/low side, latch or restart, etc etc. See this category on digikey:
    PMIC - Power Distribution Switches, Load Drivers



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    Re: Shortcircuit protection circuit

    Hi,

    until the short-circuit be removed
    As long as power is switched OFF you can not detect whether it still is short circuit or not.

    Thus I asked if you want "auto retry".

    All in all there is no cheap, reliable, simple solution ... otherwise you could buy them.

    One of the problem here is the missing specification.
    There is no immediate switch OFF. Technically there is a minimum delay. For the one application 10ms is too fast ... for another application 100ns can be too slow.

    If you hard short circuit a 24V ceramics capacitor there may be 1000 Amperes for a really short time. If you have a weak supply and a weak short circuit it just may be 2.1A...
    Itīs a huge range. Please understand that there canīt be an optimal solution for this all.

    On the other hand "very fast" is not good in any case. For example if you want to charge a capacitor it will draw a lot of current when connected. If you immediately shut of, when the capacitor is connected you will never get your application runnning.

    If you build a simple circuit .. maybe it is suitable for your current needs .. but be sure there are situations where the circuit fails. Fail in the meaning of the "short circuit protection circuit" gets killed.
    And if a protection circuit gets killed .. it is no protection circuit anymore..

    ****
    Iīve built short circuit proof power supplies up to 400V / 250A. Itīs not a simple task.
    Even not for 24V and 2A as long as you donīt know all the informations about source and load.

    Thus my recommendation:
    (Although I appreciate your idea for a restetting semiconductor solition)
    Use a simple fuse.

    And if you want it resetable one then buy a "resetable fuse" like polyfuse .. they are not precise, they are not fast, they donīt switch off completely ... but maybe a compromise...

    Klaus
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    Re: Shortcircuit protection circuit

    Thank you for your suggestion, Could you introduce me some of them if it is available in market?

    All in all there is no cheap, reliable, simple solution ... otherwise you could buy them.



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    Re: Shortcircuit protection circuit

    Google: polyfuse ..


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    Re: Shortcircuit protection circuit

    What exactly is the power supply?
    Zapper
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    Re: Shortcircuit protection circuit

    Thank you for your response. My input voltage is 24V which comes from a switching power supply.



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    Re: Shortcircuit protection circuit

    It generally requires a small voltage drop from a series shunt resistor to detect the current.
    Can you tolerate the drop caused by a 0.35Ω resistor in series with the output?

    Are you concerned about a momentary short or a continuous one?

    Do you want the current limited or turned off like a circuit breaker?
    Zapper
    Curmudgeon Elektroniker



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    Re: Shortcircuit protection circuit

    Thank you for your response.
    Yes, for dropping 2A which is equal to less than 1volt is acceptable. Continues short-circuit could damage my components and also my PCB track. Both current limiter and a turned-off circuit can help me.



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    Re: Shortcircuit protection circuit

    Here's a circuit that may be of interest.
    It's called a hiccup limiter, which turns off the output when the current goes over the limit, then periodically tries to turn back on, but stays off until the load goes below the current limit.

    The LTspice shows the limit at about 2A (blue trace) as the load resistance drops to 12Ω (yellow trace) and keeps trying (hiccup current spikes) until the resistance goes above 12Ω, where it again stays on.
    The limit can be adjusted by changing the value of R7 (which could be a 5kΩ pot if you want it adjustable.

    The P-MOSFET can be just about any with at least a 30V rating, and an on-resistance of ≦0.25Ω.

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    Zapper
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    Re: Shortcircuit protection circuit

    Addendum:
    Since the big brother moderator on this forum doesn't allow editing after a ridiculously short 30 minutes (unlike other more enlightened sites) I need to correct an error in post #14 with this added post.

    The second sentence should have said "stays off until the load goes below the current limit", not "stays off until the load goes above the limit."

    Also there should be a right parenthesis after the second to last sentence but before the period.
    Last edited by crutschow; 14th June 2019 at 01:24.
    Zapper
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    Re: Shortcircuit protection circuit

    I second the complaint about editing time frames.


    Also I'm going to plug integrated 'load switch'/'hot swap' solutions for this 24V application one more time.

    For 5V (usb), 12V or 24V at low amps it's a done deal: buy an IC to do it. It's better, cheaper, smaller and easier than almost anything else.



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    Re: Shortcircuit protection circuit

    Just to add my 2 cents.

    I recently used an integrated circuit for either detection of disconnected load or overload by using the MAX4375 (also available at Digikey), which is essentially a circuit composed of 2 comparators, where one of them conveniently uses the internal reference connected to the inverted input so that both outputs can be tied together (open collector) acting as a window detector. In the case in question, you could use one of the inputs as high current detection (alarm), and the other as a short-circuit protection (shutdown).

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