Core Selection
Powder Core Loss Calculation Core loss is generated by changing magnetic flux field within a material, since no magnetic materials exhibit perfectly efficient magnetic response. Core loss density (PL) is a function of half of the AC flux swing (½ BIBpk) and frequency (f). It can be approximated from core loss charts or the curve fit loss equation:
where a, b, c are constants determined from curve fitting, and Bpk is defined as half of the AC flux swing:
Units typically used are (mW/cm3) for PL; Tesla(T) for Bpk; and (kHz) for f. The task of core loss calculation is to determine Bpk from known design parameters.
Method 1 – Determine Bpk from DC Magnetization Curve. Bpk= f(H) Flux density (B) is a non-linear function of magnetizing field (H), which in turn is a function of winding number of turns (N), current (I), and magnetic path length (le). The value of Bpk can typically be determined by first calculating H at each AC extreme:
Units typically used are (A·T/cm) for H. From HAC max, HAC min, and the BH curve (or BH curve fit equation), BAC max, BAC min and therefore Bpk can be determined.
1.1
Flux Density, (Tesla)
1 0.9 0.8 0.7 0.6 0.5
BAC max
0.4
B
BAC min
0.3 0.2 0.1 0 1
10
HAC min
100
HAC max
800
Magnetizing Force, H(A·T/cm)
www.mag-inc.com
100 perm 50 20 10
2-8