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    Will the TVS diode protect the DC line from AC power?

    Hi,

    I have a line with a voltage of 5V DC. It is possible to supply high voltage AC (230 V) to this line.

    Will the TVS diode protect the DC line from AC?

    My TVS: LittleFuse SMBJ5.0A

    Thank you!

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  2. #2
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    Re: Will the TVS diode protect the DC line from AC power?

    The TVS will protect against excessive voltage provided the current is limited to a suitably small amount but it will not protect against the polarity reversing. For example, if the TVS clamps to ground it will try to prevent the voltage exceeding +5V and -5V so you need to be certain circuits connected to the 5V will not be damaged is the positive and negative are swapped over.

    A TVS is a clamping device, it diverts current through itself if the voltage across it is higher than its rating, therefore it has to handle all the power if the voltage is higher. You can use it to protect against 230V but bear in mind the other 225V has to be 'dumped' somewhere as heat. This is why it will only work if the current supply is small. If you intend to protect against a 5V device being connected directly to 230V AC you should look at methods to prevent the connection instead.

    Brian.
    PLEASE - no friends requests or private emails, I simply don't have time to reply to them all.
    It's better to share your questions and answers on Edaboard so we can all benefit from each others experiences.


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    Re: Will the TVS diode protect the DC line from AC power?

    Presume you have read the SMBJ5 datasheet, particularly about limiting voltage. Presumed you have a current limiting element that can withstand 230V AC (not so simple actually), you will still face a massive overvoltage which can be most likely not handled by your 5V circuit.

    In a brief, it's almost impossible to achieve the intended protection with a simple TVS diode.


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    Re: Will the TVS diode protect the DC line from AC power?

    @betwixt and @FvM, thanks for the answers!


    I'm sorry for the late reply.

    I decided to apply several solutions:

    1) Make insulating gaps between the alleged places of breakdown of high voltage to low.

    2) Use a series resistor, a high-speed fuse and a TVS diode on the relay control line.
    The resistor must limit the current so that the TVS does not explode. After its operation, the fuse must break the circuit.



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