Classification of Inductors and Introduction of Ceramic Core Inductors

Classification of Inductors

• Inductors can be categorized based on the shape of their cores into toroidal inductors, E-core inductors, and bobbin inductors;

  
  

• Based on the core material, the main types are ceramic core inductors and two major types of soft magnetic core inductors, namely ferrite and powdered iron cores;

  
  

• Based on the structure or packaging method, they can be divided into wire-wound, multilayer, and stamped inductors, with wire-wound inductors further classified into non-shielded, semi-shielded (with magnetic adhesive), and shielded inductors.

• In practical use, inductors typically include a magnetic core to achieve a larger inductance value in a smaller volume, because the magnetic core has much higher permeability compared to air. Permeability is similar to the dielectric constant in capacitors. However, due to different magnetic cores, the parameters of inductors vary significantly.

Ceramic Core Inductors

Ceramic cores are one of the common materials for inductors, primarily used to provide the supporting structure for winding the coil, also known as air core inductors. Since the core used is a non-magnetic material, it has very low temperature coefficient, making the inductance value very stable within the operating temperature range. However, due to the use of a non-magnetic material as the medium, the inductance value is very low, making it unsuitable for power converter applications.

Ferrite

Common ferrite cores used in high-frequency inductors are composed of ferrite compounds containing nickel-zinc (NiZn) or manganese-zinc (MnZn), belonging to soft magnetic materials with low coercivity. Manganese-zinc and nickel-zinc ferrites have high relative permeability, approximately 1500-15000 and 100-1000 respectively, which gives the core a high inductance value within a certain volume due to its high magnetic permeability. However, the drawback is that they have relatively low saturation current tolerance, and once the core saturates, the permeability drops sharply.

Powdered Iron Core

Powdered iron cores also belong to soft magnetic materials and are made from iron powder alloys of different materials or purely iron powder. The formulations include non-magnetic materials of varying particle sizes, resulting in a more gradual saturation curve.