Text version of the page 
Text version of the page 
| | | | | | | | | | | | | | | | | | | | | | | | POWER V | | | | | | | | | | Power Supply Magnetics Part I: Selecting Transformer/Inductor Core Material Donald E. Pauly, Consultant, Sponsored by The Arnold Engineering Company, Marengo, Illinois A review of magnetic theory and core applications from DC to 100 kHz. Materials covered include silicon steel, powdered iron, Sendust, Molypermalloy, Hi-Flux™ and ferrites. | | | | | | | | | | c \rfwitching power supply transformers and inductors require the use of high performance core materials. Choosing the proper core material for a specific application requires an understanding of core material technology. A good start on understanding the magnetic principles is magnetizing force, which is proportional to the numberofampereturnsandinversely proportional to the magnetic path length. The cgs and mks units of magnetizing force are the oersted and the ampere-turn/meter, respectively. The cgs and mks units of magnetic flux density are, respectively, the gauss and tesla. One oersted is 79.6 ampere turns/meter (250/7t)and 10,000 gauss is onetesla. Magnetic flux density is designated by B, and magnetizing force is designated by H. A flux change of 1 gauss per second over a square Cm of core area will induce 10"* volts/turn. One volt will be induced in a turn of wire that encloses one square meter of core area and whose flux density changes at one tes!a/sec. In non-magnetic materials, B is a 1 inear function of H. Iron, cobalt and | | | | | | nickel, are examples of ferromagnetic materials. When subjected to a magnetizingforce,suchmaterialsand manyoftheirailoyshavemuchhigher internal flux levels than non-magnetic materials. As the magnetizing force varies, these materials have | | varying degrees of nonlinear flux levels. The flux level of magnetic materials reaches a limit called saturation, regard I ess of how much magnetizing force is applied. Saturation flux levels of various magnetic materials | | | | | | | | | | | | | | | | | | | | | B Flux * Density 3 / | B/H Curve A n | | | | 4 / *--5 | v Magnetizing \ Force -B, | | | | | | | | | | | | | | | | | figure 1. B/H Curve ot Typical Soft Magnetic Material With Large Hysteresis. | | | | | | | | | | | | | | pom ■ 1396-1 | | | | | | | | | | | | | | | | | | | | | | | |
|