New-Tech Europe | May 2017

expressed in a considerably reduced DC resistance (RDC) of the winding. The core of WE-MAPI consists of an innovative metal alloy pressed around the winding. This gives the coil high inductance values with a small package size. At the same time, a self-shielding effect is achieved by the special construction of the core. The core material itself is temperature stable with little drift and soft saturation behavior. A protective layer is also applied around the core protecting the surface against environmental influences. Losses in power inductors The losses of power inductors are driven by a combination of core material losses and winding losses. The latter can be divided into DC current losses, principally influenced by the DC resistance of the winding (P=I2* RDC) and the AC losses (RAC) of the winding that result from skin and proximity effects. In switching controllers, the coil is one of the most important components and therefore, accurate determination of losses and heating is a key step in the selection of the right component. To predict heating, the AC losses must be accurately determined first. Here, the Dowell-, Ferreira- or Nan/Sullivan methods are just some of the methods used today. Historically, core losses were determined using the Steinmetz model, and later with a modified or generalizedSteinmetzmodel. Themain drawback of the Steinmetz equation is that it mainly applies for sinusoidal excitations and determination of the coefficients is usually only measured with small signals. However, for most applications in power electronics, the coil current is not sinusoidal. And the currents are large signals of several milliamps (mA) up to several hundred

Figure 1: Outer package and core structure: core material losses are reduced with the WE-MAPI coil

Figure 2: REDEXPERT User-Interface: the online tool calculates ideal power inductance and estimates temperature

the core and soldered or welded to the terminal with a clip. The outer shielding ring is then mounted and bonded with the inner core and the winding. WE-MAPI is different: the winding is contacted directly with

the component's connection pad without soldering and welding. By no longer requiring the clip, the effective diameter was increased, thus requiring fewer windings for the same inductance values. This is directly

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