flyback_ Design_Urgent

Discussion in 'The Projects Forum' started by Daniel_p, Mar 31, 2010.

  1. Daniel_p

    Thread Starter New Member

    Mar 31, 2010
    25
    0
    Could any body please help me with the following problem :
    Flyback transformer in discontineous mode:

    "Vin"=11-12V Dc
    "Ipeak"(primary)=520mA, ton(turn-on time)=5us
    "Lp"(primary inductance) is calculated by: Lp=(Vin*ton)/Ipeak


    A EF20 core is used with "Ae"=31mm^2 and "AL"=1200nH.
    Wire with "d"=0.38mm is used.

    Air-gap calculated by: "Lg"=[0.4*3.14*Lp*Ipeak^2*10^8]/(Ae*Bmax^2)=0.02mm
    "Bmax"=2000Gaus selected.
    Primary number of turns by: "Np"=(Bmax*Lg)(0.4*3.14*Ipeak)=8 turns
    ------
    Surprisingly the primary current taken from the power supply during the turn-on time is too small, about 100mA, expected 520mA!!
    Questions:Why is the current so small?
    Why is the inductance not equal to 100uH,it's about 80uH.
    (In each case the current is too small for Lp=80uH or 100uH)
    I'll be gratefull if any body can help me with this problem!
    thank you very much in advance