Inductive components are the heart of modern power electronics. While power transistors and diodes receive much attention, chokes and transformers largely determine efficiency, power density, EMC, thermal behavior, and reliability. Their performance depends on the core material and winding conductor, magnetic design, and cooling. Poor choices either lead to large, heavy parts (low power density) or to compact designs that overheat, both reducing the overall system performance.
Our approach: matching the magnetic co-design to the topology (e.g., totem-pole PFC, LLC, CLLLC, DAB) and the switching frequency (with SiC/GaN up into the MHz range). We combine 2D/3D FEM simulation for core and winding losses (including skin/proximity effects), thermal models, EMC assessment, and a manufacturable layout. For AC losses in high-frequency litz wires, we use modern tools (LiWiCalc®) and validate through measurements (loss/temperature rise, leakage inductance, partial-discharge/HiPot tests). On the materials side, we cover ferrites, nanocrystalline/amorphous materials, and powder cores; for windings, we select solid copper wire, copper foil, or high-frequency litz wire, depending on frequency and current. Cooling concepts (heat spreader/baseplate, potting) and automotive boundary conditions (temperature, vibration, lifetime) are integral elements.
Our design principles:
- Application-optimized magnetic design for the specific topology and load profiles
- Core shape and core material matched to the specified operating range and the mechanics of the overall system
- Winding architecture and conductor choice aligned with the relevant frequency and current range
- Thermally coherent overall design for the available cooling concept, including EMC aspects
- Result: compact, efficient, and robust inductive components for OBCs and demanding custom power supplies, from concept to prototyping with our manufacturing partners - get in touch with us.
The Magnetic Material and Core Geometry
Magnetic cores and materials come in a great variety – as do established, standardized core shapes. Thanks to our expertise in charger and power‑supply topologies (e.g., totem‑pole PFC, LLC, DAB), we select the right core geometry and optimal material for your requirements. A rapid preliminary analysis of flux density and core losses in 2D FEM is complemented by detailed 3D simulation that accurately represents air gaps, winding layout/layer build‑up, stray fields, and parasitic elements.
Standard cores do not always deliver the optimum. When installation space, cooling concept, insulation clearances, or target efficiency require it, we develop application‑specific cores. The result is compact, low‑loss, and production‑ready solutions, tailored to automotive boundary conditions (temperature, vibration, service life).
We work with all common materials: ferrites for high switching frequencies, nanocrystalline/amorphous materials for low losses at high flux densities, and powder cores for chokes with high current capability. Depending on the application, we integrate conductive thermal paths (baseplate/heat spreader), potting (encapsulation), and account for creepage/clearance distances as well as standards compliance.
The Winding Material – Solid Wire, Foil, or HF litz wire
In our chargers and custom switch-mode power supplies, the choice of windings also determines efficiency, size, and EMC. The appropriate winding material – whether solid copper wire, copper foil, or high-frequency litz wire – must be tailored to the application, output power, and switching frequency. While solid-wire or foil windings can be readily evaluated for AC losses using established FEM tools, high-frequency litz wire presents specific challenges: it consists of many individually insulated strands that are bundled and twisted together. Selecting the optimal litz construction and the right number of strands is essential to control skin and proximity effects and minimize high-frequency winding losses.
Our team at Fraunhofer IISB has many years of experience in designing inductive components – from PFC chokes to OBC transformers. For every topology and switching frequency, we choose the appropriate litz wire and define geometry, layer build-up, and insulation, with a focus on efficiency, thermal behavior, EMC, and manufacturability. In addition to our own calculation tools, we use LiWiCalc® for accurate determination of litz losses and validate the results through simulation and measurement.
Fraunhofer Institute for Integrated Systems and Device Technology IISB
