• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 769 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Doubts regarding the minimum number of primary Turn equation

Aneesh TS
Expert 1735 points

Hi Friends,

  I have doubt regarding the transformer turns equation. The transformer equation which is mentioned in magnetic inc document for square wave is  E=4B*Ac*N*Fs x 10-8 (square wave). But while designing transformer minimum number of turns every document follows the equation N=(E*D/Ac*B*Fs)

Where E=Voltage

B=Flux density

Ac=Core area

N=Number of turns

Fs=Switching frequency


If we give same values to both equation we will get different number of turns. Why this difference has come?. Which is the right equation?. Can anybody explain me the reason?

Regards

Aneesh

  • 0
    TI__Genius 9130 points

    Aneesh,

    I think the 2 equations are probably equivalent, except that Mag Inc are probably using antiquated units of Gauss & Oersted instead of SI units Tesla and A/m. There may also be an assumed value for max duty cycle D. You really need to query the Mag Inc eqn with them.

    The basic equation comes from Farady's Law:

    E = N * d(phi)/dt

    [sorry this editor does not support symbol font, so I can't use the Greek symbol for flux).

    I.e. E = N * Ac * dB/dt = N * Ac * Bpk * D * fsw

    I hope this helps. If so, please click the "verify answer" button.

    Thanks,

    Bernard

  • 0 in reply to Bernard Keogh
    Expert 1735 points
    Hi Bernard,

    Please note the units given by magnetic Inc for their equation E=4B*Ac*N*Fs x 10-8 (square wave).

    E=applied voltage (rms)
    B=flux density in gauss
    Ac=core area in cm2
    N=number of turns
    F=frequency in Hz

    1. Magnetic inc has mentioned their B is in Gauss. But Gauss to tesla conversion is just a matter of 10th power. And there is no Field intensity(H) term in the equation. So the Oersted to A/m conversion will not come,
    2. two equations are differ by a multiplication factor of 4. ie if you get 20T with first equation you will get 5T with second equation. This is not a small difference. Its a huge difference.
    3. If they assume Duty cycle for square wave as 0.5 Then also the two equations differ my a multiple factor of 2.
    4. And not only Magnetic Inc i have seen this equation(E=4B*Ac*N*Fs x 10-8 (square wave)) in some other documents also.

    Regards
    Aneesh
  • 0 in reply to Aneesh TS
    TI__Genius 9130 points
    Aneesh,

    As I said above, you really need to query Mag Inc about their own equation.

    The 10^-8 factor comes form the G vs. T and cm^2 vs m^2.

    The factor of 4 may be due to the assumption of 50% duty cycle, and maybe assuem that B is actually Bpk-pk rather than Bpk? Just speculation.

    In any event, if you follow Farady's Law, you can't go wrong.

    Thanks,
    Bernard