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  1. #1
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    Toroids EMI suppression choce choice of core material ?

    Hello,

    I have 25V DC line which power RF power amplifier on 15MHz current is about 1A.
    And I need inductor to LPF for suppression all EMI from 15MHz PA from the 25V DC source.
    According to calculations I need inductor about 700uH.

    Toroidal cores can be used on the coil

    Core N L Lenght d DC R XL Flux price
    T37-75 18 712uH 20cm 0,7mm 92mOhm 67,1 kOhm 28G 1
    T50-43 43 693uH 66cm 0,5mm 667mohm 65,9 kOhm 7G 2

    Solution with T37-75 is smaller, have less resistence, half price and lower labor intensity (only 18 turns)
    The question is whether 75 is suitable for this use?

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  2. #2
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    Re: Toroids EMI suppression choce choice of core material ?

    As an inductor you can use either one. Obviously the smaller one is cheaper and equally effective.

    But you do not mention the power to be handled.

    Yes, a lot of power is going to come back to the power supply rails. You want to block the power that gets on the power supply.

    If your design is good, you should rate about 10-20% of the power (RF power output) to be handled by the choke. But the amplifier design may be inspected carefully to prevent RF to come back to the DC line.

    In absence of other details, you need to experiment.



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  3. #3
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    Re: Toroids EMI suppression choce choice of core material ?

    Quote Originally Posted by carpenter View Post
    Hello,

    I have 25V DC line which power RF power amplifier on 15MHz current is about 1A.
    And I need inductor to LPF for suppression all EMI from 15MHz PA from the 25V DC source.
    According to calculations I need inductor about 700uH.

    Toroidal cores can be used on the coil

    Core N L Lenght d DC R XL Flux price
    T37-75 18 712uH 20cm 0,7mm 92mOhm 67,1 kOhm 28G 1
    T50-43 43 693uH 66cm 0,5mm 667mohm 65,9 kOhm 7G 2

    Solution with T37-75 is smaller, have less resistence, half price and lower labor intensity (only 18 turns)
    The question is whether 75 is suitable for this use?
    You can't use the specificed AL value at the frequency of 15 MHz to calculate the number of turns. If you have a look to the permeability vs. frequency graph you can see that at your frequency the ur' is not specified and should be very low (around unity). So the 75 material is not suitable for your purpose.
    The other material (43) seems instead to be OK. Also in this case you can't use the given AL value to calculate the number of turnns, since at 15 MHz the ur' drops significatively (from 750 down to 200) so you have to correct AL by the ration of the two ur' values (i.e. approx 200/750). Furthermore the core losses (ur''), at 15 MHz, will be incresed roughly by a factor 20x (have a look to the graph in the datasheet).

    You can try to reduce the dimension by using a smaller toroid made by 43 material, if it can widhtstand both the dissipation due to the power losses and the DC current flowing.



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  4. #4
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    Re: Toroids EMI suppression choce choice of core material ?

    You're right. To calculate the inductance I used mini Ring-Core-Calculator
    I assumed he was working with true permeability, big mistake, even sw widespread among radio amateurs counts incorrectly.

    OK I will have to use T50-43.
    is attacking someone with better material available at www.mouser.com ?

    Is there any mini Ring-Core-Calculator-like program that can count on true permeability?



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