Because the AL-value is often set as a design specification and AL-value is a nonlinear magnetic property of the core, it varies widely according to the making current. Finite element analysis (FEA) enables accurate reflection of magnetic properties, and so can obtain AL-value current properties and provide feedback for design.
This note presents the use of a magnetic field analysis to obtain the AL-value current properties of a choke coil.
Magnetic Flux Density, Flux Linkage, and AL-value
The magnetic flux density distributions of the core for currents of 0.5 A and 0.7 A are indicated in fig. 1, the current characteristics of the flux linkage are indicated in fig. 2, and the current characteristics for the AL-value are indicated in fig. 3. If the current flowing in the coil increases, the flux linkage increases only minimally because of magnetic saturation in the core. Furthermore, the AL-value is smaller due to magnetic saturation in areas where the current is large because the AL-value is the inductance per turn in the coil.