The magnetic design of acdc power module

acdc power moduleThe reliability of the magnetic core is another issue that is often overlooked. Most output inductors use powdered iron cores because powdered iron is a low-cost material. About 95% of the iron core is pure iron particles, which are combined with organic glue. The glue also separates each iron particle, so that the core is filled with air-permeable spaces inside and outside.

Iron powder is the raw material that makes up the core. However, iron powder contains a small amount of impurities such as manganese and chromium, and these impurities affect the reliability of the magnetic core depending on the amount of impurities contained therein. We can use a cross-sectional electron microscope (SEM) to carefully observe the core to determine the relative distribution of impurities. The core is reliability. The key is whether the materials can be predicted and whether the supply is stable and reliable.

If the iron powder core is exposed to a high temperature environment for a long time, the iron loss may increase. Once the loss increases, the iron loss will not recover due to the molecular decomposition of the organic binder and the increase in eddy current loss. This phenomenon can be called thermal aging and may lead to thermal control cores.

The size of the core loss is affected by many factors, such as AC magnetic flux density, operating frequency, core size and material type. Taking high-frequency operation as an example, most of the losses are eddy current losses. If it runs at low frequencies, the hysteresis loss is a large loss instead.

Eddy current losses cause the core to heat up and affect efficiency. Eddy current loss occurs because the object caused by the ferromagnetic substance is subjected to different magnetic fluxes at different times, causing the object to produce a continuous current flow. As long as we use a ferromagnetic sheet instead of solid ferromagnetic material as the magnetic core, the eddy current loss can be reduced. For example, Metglas, which surrounds magnetic tape, is such a core. Other suppliers of ferromagnetic products also produce tapes that are wound tapes.