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    FCC conducted emissions question

    Hi,

    I had a device that was failing with the conducted emissions test of the FCC part 15b.

    It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

    My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

    I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

    Thanks

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    Re: FCC conducted emissions question

    pls refer the attach pdf....

    do not forget to press help me button


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    Re: FCC conducted emissions question

    Just place C6 100nF (X2 type) before D1. Or add new one (better)

    Quote Originally Posted by difflvl
    Hi,

    I had a device that was failing with the conducted emissions test of the FCC part 15b.

    It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

    My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

    I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

    Thanks



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    Re: FCC conducted emissions question

    Quote Originally Posted by BasePointer
    Just place C6 100nF (X2 type) before D1. Or add new one (better)

    Quote Originally Posted by difflvl
    Hi,

    I had a device that was failing with the conducted emissions test of the FCC part 15b.

    It was failing in the 800khz-1.2MHz range. I do not have a clock source of that frequency on my board, nor was I able to trace where it is coming from.

    My question is this what can I add to my power supply circuit to reduce noise in the 1MHz region.

    I have attached my power supply schematic below. It is a 3.3 V regulator with VIN being a 6volt wall wart.

    Thanks
    6 100nf caps will help with the 1mhz frequency range? I thought those values are good for higher frequencies. At the lab I tried adding more 100nfs and it didn't really do anything.



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    Re: FCC conducted emissions question

    - What is your input voltage?
    - What is the output current that you require?
    - Does the power supplier have a load when testing?

    You may use higher capacitor instead of 100nF (X2). For example electrolytic one.
    Can you send graphical test output here?



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    FCC conducted emissions question

    The input voltage is 6VDC from a wall wart. Output current required is ~200-450mA. Yes it has load during testing.

    I don't have the test output available but I was 18dBs over the limit at ~1MHz.



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    Re: FCC conducted emissions question

    What clock sources are there in you design?



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    Re: FCC conducted emissions question

    Clock sources are 14.7456mhz from crystal, 28.224mhz from another crystal and 4.032mhz from an IC.



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    Re: FCC conducted emissions question

    Quote Originally Posted by difflvl
    Clock sources are 14.7456mhz from crystal, 28.224mhz from another crystal and 4.032mhz from an IC.
    Did you try 100uF/25V or 1000uF/25V electrolytic instead of C6 100nF?


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    Re: FCC conducted emissions question

    Hi, reading the hole topic it seems like the wall wart power supply is causing problems. I might be wrong here. Are you are testing with the wall wart power supply to get a compliance certificate for the complete system. Perhaps you can try an other power supply if the one you are using is a switching power supply. It might be market CE and all the rest but most of them are not. I'm currently evaluating power supplies from china for a product. Some of them even fail on the input voltage requirement of 85 volt...

    Regards



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    Re: FCC conducted emissions question

    If possible ( cost available ), add an emc coil at test port. It has significant improvement.

    Rogerynt



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    Re: FCC conducted emissions question

    Quote Originally Posted by inventor(y)
    Hi, reading the hole topic it seems like the wall wart power supply is causing problems. I might be wrong here. Are you are testing with the wall wart power supply to get a compliance certificate for the complete system. Perhaps you can try an other power supply if the one you are using is a switching power supply. It might be market CE and all the rest but most of them are not. I'm currently evaluating power supplies from china for a product. Some of them even fail on the input voltage requirement of 85 volt...

    Regards
    If you have a list of a few wall warts that are good I would appreciate it.



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    Re: FCC conducted emissions question

    difflvl, at the moment I have tried three different brands. But I can't test radiated emission. I don't have the equipment to do this. Here my customer is a bit upset about the price he has to pay to get a certificate...
    Anyway, a good working and very low cost power supply can be found on: cnhitong.com


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    FCC conducted emissions question

    Thanks alot.



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    Re: FCC conducted emissions question

    Hi
    you can try this method also put ferrite bead in series with the input power jack to reduce the conducted emission problem



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