Inductor application characteristics

inductance

The figure below is the equivalent circuit of the actual inductor. Where L is the ideal inductance of the device. RW is the series resistance caused by the winding itself and the terminal, RI is the equivalent parallel resistance caused by hysteresis loss, and C is the inherent capacitance of the winding.

In order to reduce the inherent capacitance of the inductor C. Usually the coil windings are not wound directly onto the core. In addition to mechanical instability, the extremely high dielectric constant of the core increases the inherent capacitance of the winding. If the two are in close contact, the C value will multiply. The bobbin can be used to support the windings and provide a good separation between the windings and the core to minimize the inherent capacitance. In addition, the winding method of the winding also affects the size of the inherent capacitance: the single-layer winding has the lowest inherent capacitance, and the multilayer winding can reduce the inherent capacitance by "irregular" winding or by using a multi-section bobbin.

To get a large L value, the inductor uses a magnetic core with a high magnetic permeability. However, the use of high magnetic permeability materials, on the one hand, introduces its own hysteresis loss RI. On the other hand, this material reduces the magnetic permeability as the magnetic field increases, so-called "saturation" phenomenon, which means Under the action of high bias current, the inductance L value will decrease. Therefore, in the application, the inductors with different core characteristics should be selected according to the different requirements of the circuit. Widely used magnetic core materials are manganese zinc ferrite, nickel zinc ferrite and iron powder. Mn-Zn ferrite has a higher magnetic permeability, but the loss increases rapidly with increasing frequency: nickel-zinc ferrite has low magnetic permeability, but has low high-frequency loss: the magnetic permeability of iron powder is the largest. 30 or so, but another feature of it is very difficult to saturate.