What is Leakage inductance

Leakage inductance refers to the leakage inductance in a transformer due to the incomplete closure of the magnetic flux. It is also often understood as: the part of the magnetic flux that is missed in the coupling process of the transformer's primary stage, so it is called leakage induction.

Leakage inductance is an important parameter of transformer, which has an important influence on the efficiency and performance of transformer. We often say that the leakage inductance refers to the leakage inductance of the main winding, this article is also from this to explain.

Leakage will increase with the increase of frequency, in the high frequency operating state, leakage can not be ignored. It will not only cause radiation interference in the circuit, but also bring noise to the whole power supply. What's more, the existence of leakage inductance causes the transformer to switch instantaneously, generating a reaction electromotive force, and too much leakage inductance can easily lead to overvoltage breakdown of related components.

Therefore, in the transformer, we need to reduce leakage by design.

Miss the influence of many factors. The biggest impact is the magnetic core structure, if the magnetic core does not need an air gap, then as far as possible the use of closed ring and square structure of the magnetic core, to help reduce leakage.

Secondly, the structure and shape of the winding also have a great influence on the leakage inductance, such as the number of main winding, winding turn ratio, winding width, winding layer number and so on. In the transformer, increasing the width of the winding can reduce the leakage induction, and this is the reason for the common winding when the secondary winding number is small; The sandwich winding law is to change the winding structure, in the PQ transformer, the sandwich winding method can control the leakage induction within 1% of the inductance.

In addition, the depth and width of the air gap also affect the leakage induction of the transformer. Under normal circumstances, we commonly use the core column to open the air gap to reduce the leakage of the transformer.

Of course, leakage isn't always harmful. In the design of LLC resonant transformer, we often replace the resonant inductor by increasing the leakage inductance, and one resonant inductor can be reduced in the circuit, thus reducing the cost.

In this design, a two-slot skeleton is used to separate the primary and secondary coils. By using the baffle between the two slots, the primary and secondary windings can be separated effectively, and the leakage induction can be increased synchronously and effectively while ensuring the safety distance.

If the leakage sensation is still unable to meet the requirements, the retaining wall can also be increased on the side of the baffle to further increase the distance between the primary windings, thereby increasing the leakage sensation. In addition, by increasing the number of main winding, it is also an effective means to increase the leakage inductance.