New-Tech Europe | May 2017

amperes (A). There are other models that attempt to tackle the problemof non-sinusoidal waveforms by separating hysteresis and eddy current losses. The empirical Steinmetz equation has proven to be a useful variant, but offers high accuracy only for sinusoidal currents. However, the various Steinmetz models only work optimally with a duty cycle of 50 percent and within a limited frequency range. Moreover, determining the magnetic path length is highly complex. Subsequently the determination of core losses with the help of existing models for iron powder and metal alloys is not only demanding, but the accuracy is also subject to significant fluctuations. For inductors that consist of several different core materials, an estimation of the losses is not possible, or at the very least highly complicated. Empirical data-based AC- loss model Würth Elektronik eiSos has developed a sophisticated model capable of accurately measuring the complete AC losses in inductors. It is based on empirical data generated by real-time application set-ups. Here the total losses of the inductor are divided into AC- and DC-losses. Empirical data is captured with a DC/DC converter. A pulsed voltage is applied to the inductor, whereby

range so that extreme scenarios can be taken into consideration. This allows the most energy-efficient power inductor to be selected for the respective application. To determine the right inductor for a buck converter, the existing input voltage range and the output voltage and current are entered into the user-interface, as well as switching frequency, diode flow voltage and targeted ripple current of the inductor. A simple click on "Display Details" reveals the most suitable power inductor, including its anticipated ripple currents and the losses in the application. A manual loss calculator is also available to determine the losses for power inductors independent of the topology. Only frequency, duty cycle and ripple current, or voltage drop, need to be entered and REDEXPERT takes care of the rest. A useful feature immediately displays the entries graphically below the data entry screen. As REDEXPERT is a web-based tool, there is no need to download or worry about updating the tool. Registered users have access to further features, such as determination of inductance value or temperature increase of the inductor for every possible current value.

the input power Pin and the output power Pout are measured. On this basis Ploss = Pin - Pout is determined and the AC losses of the coil PAC are separated. This procedure is used to measure and capture empirical data for various parameter settings such as fluctuations in the magnetic modulation, switching frequency, ripple current, etc. A model for the calculation of the AC losses is then created with the use of this empirical data. Determining losses online REDEXPERT is an online design tool from Würth Elektronik eiSos to select the most suitable power inductor for the respective application. It is an intuitive and effective tool that enables component comparison at the click of a button. The calculation of AC losses in magnetic components is just as critical as it is complex - but not with REDEXPERT, as the AC loss model from Würth Elektronik is integrated into the tool. The calculation accuracy of the complete AC losses also makes the application suitable for temperature estimation. Currently three topologies are supported in which the component can be selected for the application: buck, boost and SEPIC converters. The losses are displayed graphically over the complete input voltage

Advantages of the AC loss model:

Empirical data is based on a DC/DC converter Accurate determination of losses for every given duty cycle Accurate across a wide frequency range (10 kHz to 10 MHz) Considers the smallest changes in the core material and the winding structure

Applicable for components where more than one material is used Accurate determination of losses in components with iron powder and metal alloys Applicable for every possible core design and winding structure Includes AC winding losses

New-Tech Magazine Europe l 19