Litz wire

Litz, also HF wire, a wire, which is fine from a larger number, usually by coating each other insulated wires that are so intertwined that on average each individual wire as possible every place in the total cross section of the strand equally often occupies. The application of this strand is in the range of high frequency technology.

Description

To be fully effective, none of the fine wire strands may be interrupted, and all wires must be stripped at each end and connected to the circuit, as this will degrade the quality. In this manner all the individual conductors are connected in parallel.

The higher quality in the high frequency range is due to the increase of the effective participating in the current flow cross-section, which is limited by the following effects in solid wire:

• Skin effect ( charge carriers due to displacement of the magnetic field of single line ). At high frequencies, due to this effect, most of the current flows along or near the surface of the conductor. For example, at a frequency of 10 MHz, the power density of 20 microns below the surface of only the 1/e-ten part (37 %) of the current density on the outermost surface. By increasing the specific conductivity of the surface of the leakage resistance can be lowered.
• Proximity effect ( charge carrier displacement on one side of the conductor through the magnetic field of a coil made ​​from them )

Application

Litz is used eg for the production of coils for resonant circuits and partly in switching power supplies and storage chokes. Compared with solid wire, it has the advantage of lower power losses at higher frequencies and thus permits a higher quality of manufactured therefrom coils. By dividing into stranded wires while the fill factor is degraded compared to the non-split cross-section, the advantage by interweaving more than offset the loss cross section again. It is therefore necessary to determine for each application the optimal stranding.

Typical applications are found primarily in the medium and short wave range, for example, for winding of ferrite rod.

In the low frequency range, and also in the long-wave skin effect plays with small conductor cross-sections not matter much, since the skin depth is equal to or greater than the wire diameter. Litz but is often used in switching power supply transformers and chokes as well as getting in induction cooking coils. Here, the cross sections are so large that even in the lower high-frequency range ( from 20 kHz) losses would occur.

In the ultra-short wave range, the cable lengths because of the lower number of turns are small. In addition, the advantages of the HF wire be canceled by capacitive shunts in this frequency range. Therefore, no Litz will be used.