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Inductor - 4 Pins???

Discussion in 'General Electronics Discussion' started by Lord_grezington, Jun 3, 2013.

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  1. Lord_grezington

    Lord_grezington

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    May 3, 2013
    Hello

    I have decided to use this component http://uk.farnell.com/multicomp/mct...de-85uh-12a/dp/1864499?Ntt=MCT25X12X15C-850PU Its great as the cost ok, but it has 4 pins. There is a 85mH inductance between 1-4 and also a 85mH inductance between 2-3.

    Does this mean that I can use them in either a series or parallel configuration? or even better, can I use the 85mH Inductance for 2 completely different circuits? I expect not due to transients and harmonics - but it would be good to hear it from someone in the know.

    Graham
     
  2. davenn

    davenn Moderator

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    Sep 5, 2009
    Hi Graham

    what are you wanting to use this in ?

    This particular choke would normally be used in a power supply along with a couple of capacitors for filtering
    is that your intent ?

    Dave
     
  3. duke37

    duke37

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    Jan 9, 2011
    88mH pot cores used to be used to load telephone lines and many became available on the surplus market.

    They were often used to make audio filters for RTTY.
     
  4. BobK

    BobK

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    Jan 5, 2010
    You cannot use them as separate inductors since they are magnetically coupled and each will affect the other.

    You can put them in parallel and get twice the current capability at 85uH or you can put them in series and get 340uH at the rated current. The polarity must be correct in either case, or they will cancel each other.

    Bob
     
  5. Lord_grezington

    Lord_grezington

    124
    2
    May 3, 2013
    Thanks Bob - you have confirmed what I would have expected.

    Dave - yes, I will be coupling it up with a couple of capacitors. Its going to be used in a buck converter.

    Graham
     
  6. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

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    Jan 21, 2010
    Given that they're a common mode choke, placing them in series or parallel may saturate the core fairly quickly.

    I believe in normal use the current in each coil opposes the other so no net magnetic field is generated. When there is an imbalance in the currents a net field is created and the change in current is opposed. Thus the normal flux density in the core is quite low.

    That's my understanding, but I might be quite wrong.
     
  7. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
  8. Lord_grezington

    Lord_grezington

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    May 3, 2013
    Hi

    I think this inductor (and project) is slightly different. The data sheet for the inductor states 12Adc. I get what your putting across with the two coils balancing the current or flux in the core. http://www.farnell.com/datasheets/1328591.pdf

    But, just to make sure i have things clear:

    1. I can use one half of the coil as a standard inductor
    2. The inductor (or choke) is design to be used with the coil apposing each other so that if one coil had a larger ripple than the other it will cancel out.
    3. I can use the coils in series, as long as i did not exceed 12A.
    4. I cant use the coils in parallel as this will not improve current rating as the coil will saturate (at the rated 12A).

    I think a true or false answer to the four above questions should let me progress with the project.

    Graham
     
  9. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    To my knowledge, none of those statements is correct. The common-mode choke is designed to have equal and opposite currents flowing in the two halves. This prevents the core from saturating, so it remains inductive and is able to present a relatively high impedance to high-frequency common-mode voltages. Unless there is an equal and opposite current in the two coils at all times, the core will saturate. If you connect the coils in anti-parallel or anti-series, you will avoid saturation, but you will also avoid the inductance (the only inductance you get will be leakage inductance). This is all AFAIK; it's outside my experience.
     
  10. Lord_grezington

    Lord_grezington

    124
    2
    May 3, 2013
  11. KrisBlueNZ

    KrisBlueNZ Sadly passed away in 2015

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    Nov 28, 2011
    Yes, that's the kind of inductor to use in a switching power supply. It will be fine at 100 kHz.

    Don't worry about the fact that the frequencies specified on the Farnell page aren't 100 kHz. The Q test frequency is just the frequency they used to measure the Q (quality factor) of the inductor, and the self-resonant frequency is just the frequency that it will resonate at (using its own parasitic capacitance). Neither of these affect its ability to operate at 100 kHz.

    Edit: They're also available in 68 uH and 100 uH inductances if that would be better. (I mention this because you originally wanted to use an inductance of 85 uH.)
     
    Last edited: Jun 8, 2013
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