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    Inrush current limiter

    Hello,

    I have a 24V/6A dc power supply. When I apply this power supply to my circuit ( a diode bridge and 470MF capacitor) it produces sparks. I am going to use a NTC (about 10ohm). Based on my space limitation I can't use a relay to bypass this NTC after a second. I am worried about placing the NTC in my circuit. Because my steady-current is approximately about 2.5A which NTC wastes about 62.5W.

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    What is your idea?

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    Re: Inrush current limiter

    ... and your thermistor tries to drop 2.5 * 10 = 25V as well.

    First explain what you mean by "it produces sparks" as this is nothing to do with inrush current.

    Brian.
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    Re: Inrush current limiter

    Thanks for your comment and swift response.
    I put a power connector on my PCB. When I connect the power to it at first glance, because my Cap is empty, it produces a spark at my connector. In addition I am worried about the life time of my component such as my diode bridge and my power supply in this configuration. How can I decrease or protect my circuit?



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    Re: Inrush current limiter

    Most components are rated to handle higher current for brief periods so I doubt any damage would occur in any case.
    There are methods to limit the charge current to a capacitor but if the load is 2.5A the 'spike' caused by the capacitor charging will be fairly small compared to the steady background current. Are you sure the capacitor is actually the cause of it?

    Another consideration is how your load (the PCB) will react if the current is limited. A limit to the current means the voltage will rise slower and some circuits may not reset cleanly or even start at all. Can you briefly tell us what the PCB does please.

    Brian.
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    Re: Inrush current limiter

    Thank you very much for your comment.
    My PCB consists of a micro-controller and some optocoupler to enable and disable some 24V output switch (10mA). However, my main load is a motor driver which use 2A to biases itself. In my test, I disconnected my motor driver and my circuit just consumes less than 300mA. So in my circuit the first capacitor which is 470microF takes much current at the first time.



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    Re: Inrush current limiter

    For 24V you may be best off with a current limiting IC, or 'load switch' or 'soft start controller'.

    FPF2700 is one example in this category.

    It's also possible to use a simple discrete circuit:
    https://electronics.stackexchange.co...rrent-limiting


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    Re: Inrush current limiter

    A cheaper alternative might be a low-Q inductance in series with the incoming power. Something like a 50 - 100uH choke with a ~22 Ohm resistor across it. The inductor will slow the current rise and the resistor will damp its Q to prevent excessive ringing.

    Brian.
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    Re: Inrush current limiter

    Because my steady-current is approximately about 2.5A which NTC wastes about 62.5W.
    Surely wrong. The hot NTC will be possibly drop 0.5 or 1 V, thus 1 - 2.5 W losses.



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