Many electronics engineers have been in the situation where they need to design a switched-mode power supply. It’s not too much of a problem these days because there are plenty of ICs around from different IC manufacturers that can do all the hard work. There are usually online design tools and simulators to assist you with the design. When it comes to the Inductive components in the design however there are many factors to take into account to optimize the design and often little help available. Now there is a new online tool called REDEXPERT from Würth Elektronik eiSos, the specialist for inductive components.

Power losses in switched-mode power supplies take place mostly in the inductive components and power semiconductors. Losses in inductive components occur in the core and windings. To design a reliable and efficient power supply it’s important to keep these losses as small as possible. To estimate the core losses in a switching power supply requires a complex measurement setup and it’s not guaranteed that the estimate will be relevant to the specific application.

Core losses can be calculated using steinmetz’s equation and its extensions but these are only applicable under certain conditions and when using certain materials. Würth Elektronik eiSos has now developed a new state-of-the-art model that can be used to determine core losses effectively and accurately. This model has been implemented in the new REDEXPERT tool where you can even choose your preferred language from the 7 available.
Buck-converter example

An article by Ranjith Bramanpalli, introducing the use of REDEXPERT, is published in the September/October edition of Elektor. The screenshot above is, for example, a step-down converter design. The input voltage is 8 to 12 V with 5 V output. Other parameters are 800 kHz switching frequency, ripple current = 40% and output current of 1 A. Given these values, REDEXPERT calculated an optimal inductance Lopt of 9.6 μH, ON time of 550 ns with a 0.44 duty cycle. For this example, more than 200 products were recommended. If you want to use a very small and low-loss storage inductor, one from the WE-MAPI series is a good choice.

The Würth Elektronik model was extensively empirically validated and compared with existing models and measured data. Alternating current losses for various materials, such as WE superflux, iron powder, NiZn, MnZn, etc., were measured over large duty cycle and frequency ranges and compared with theoretical models.