The peak AC flux density is 670 G at 80 kHz produces a core loss of 4.9 W. The core selected is part number T106-52 wound with 14 turns of AWG-14 resulting in 1.72 W of copper loss. The maximum ambient temperature is 60☌ with forced air cooling supplied by a variable speed fan that provides less air flow at lower power levels. The first design example is for a buck inductor operating at 80 kHz. This design utilizes a core that can not safely dissipate the high level of core loss even with the benefit of forced air. The first example will illustrate what happens in a design that is dominated by core loss and uses an undersized core. It is the eddy current portion of the core loss which is affected by high temperature thermal aging. The contribution of each form of loss to the total is also affected by the operating flux density. Eddy current loss will be the dominant loss at higher frequencies while hysteresis loss will be the dominate loss at lower frequencies.

The extent of these changes and realized effect on the wound core are a function of the following variables time, ambient temperature and air flow, core volume and shape, operating frequency, peak ac flux density, material type and core manufacturer. Thermal aging is an irreversible increase in core loss as a result of prolonged exposure to elevated temperatures. It is important for the design engineer to understand the conditions under which thermal aging can occur and incorporate this knowledge into their standard design process. All iron powder cores, regardless of the manufacturer, are susceptible to permanent increases in core loss when exposed to elevated temperatures for extended periods of time. The following discussion and examples illustrate the phenomenon of thermal aging and detail the variables and conditions that effect a change in core loss characteristics.

Air core inductor calculator 14 awg