B64290 series ring ferrite cores from TDK and their uses


Inductive elements are an important component of electronic and electrical circuits. One of the simplest and most significant ways to increase the inductance and improve the characteristics of inductive elements is the use of specially shaped cores made of materials with special magnetic properties.

One of the popular core types in TDK's products is B64290 series toroidal ring cores. The entire product line includes a wide range of ring cores ranging in diameter from 2.5 to 202 mm.

Appearance of B64290 series ring core

A typical application for NiZn alloy cores is chokes for use in a wired local area network (LAN) with a K10 core material from TDK. For EMI suppression in other applications, it is more preferable to use MnZn alloy cores with the following diameters:

  • Diameter from 2.5 to 12.5 mm is more preferable to use for telecommunication lines (material type N30, T38, T46);
  • 13.3mm to 26mm diameter is more suitable for chokes in power lines (material type N30, T65, T35, T37, T38);
  • Diameter over 34 mm - for chokes and filters for industrial use in power lines (type T65).

TDK manufactures ring cores in a variety of coating options to find the right solution for any application. The coating not only provides protection for the edges of the core, but also performs an insulating function. For small ring cores (for small diameters up to 9.53 mm) , a parylene coating is used, which is distinguished by its low thickness and high dielectric strength. The second type of coating used, for cores of medium and large sizes (over 9.53 mm) is epoxy resin. Between themselves, both types of coating differ in color: the parylene coating is colorless, and the epoxy coating has a blue color.

Ring cores are mainly used as matching transformers and electromagnetic chokes to suppress radio frequency interference in the MHz range:

  1. When designing a matching (signal) transformer in a wired local area network (LAN) signal with a transformation ratio of 1: 1, small toroidal ring cores are usually used. The function of such a transformer is to match the impedance of the line and the network termination (user equipment).
  2. Current-compensated chokes must be used to suppress common-mode interference also in a wired LAN in the frequency range from 30 MHz to 300 MHz . The corresponding type of ferrite material is K10, which is a NiZn material with a permeability of about 700 for parylene coated small cores. The impedance versus frequency curve of the K10 is perfectly adapted to the suppression requirements in a local network: Normalized impedance versus frequency curve for R10 core (2 turns)
  3. To protect against electromagnetic interference (EMI), toroidal ring cores are also used to create a common mode choke. Compact electrical and electronic equipment primarily generates common mode noise. To meet safety requirements (without exceeding the allowable leakage current), it is necessary to use chokes with a high asymmetrical effective inductance. For this purpose, it is advisable to use chokes with current compensation and closed core topology. The problem of saturation of the core material due to useful current is solved in this design by winding two windings (actually coils on each line of the differential pair) with an equal number of turns per core. These windings are connected in such a way that the magnetic flux induced by the top winding is compensated by the bottom one.
The principle of operation of a common mode choke

Since the differential useful signal is a pair of signals with usually equal amplitudes, but different phases (rotated relative to each other by 180°), when the differential signal passes through the common mode choke, each of its components creates a magnetic flux of different polarity. These flows cancel each other, which makes the inductor transparent to the differential signal (in practice, with little loss of the useful signal). A common-mode signal from a source of distributed interference is formed by two signals with equal amplitude and the same phase. When it passes through the common mode choke, the magnetic fluxes of the two signals are added in the ferrite core, the impedance of the choke increases, which leads to a significant suppression of the common mode signal.

For more detailed technical specifications of B64290 toroidal ring cores from TDK, see the Specification.