High-Frequency Litz Wires for Switched-Mode Power Supply Transformers: Efficiency in Industrial Electronics
In a joint development project, PACK LitzWire supported an industrial customer in modernizing the transformers of its switched-mode power supplies. The goal was to reduce installation space requirements while increasing efficiency at high switching frequencies. The devices typically operated at frequencies above 100 kHz and had to meet strict standards such as EN 62368, EN 61558, or EN 60601.
The Challenge
The compact transformers had to handle high power densities in cramped housings. Conventional round wire windings reached their limits:
- Electromagnetic: Skin and proximity effects led to high AC losses and thus to excessive heating.
- Thermal: The limited surface area for heat dissipation in the dense housings intensified the thermal management challenges.
- Normative: Despite the compact design, the optimized winding had to meet all requirements regarding insulation, dielectric strength, and creepage distances.
The customer therefore needed a winding structure that could efficiently handle high frequencies without increasing the size of the transformer or exceeding thermal limits.
The original transformer winding with conventional conductor geometry shows structural limits at high switching frequencies: increased AC losses, higher heating, and limited efficiency in a compact format.
The optimized winding with HF litz wire significantly reduces skin and proximity effects, enabling a more compact and thermally stable transformer with higher efficiency and standard-compliant insulation.
Solution Strategy
PACK LitzWire developed, in collaboration with the customer, a winding design optimized for high frequency.
- Litz Wire Recommendation: Fine-stranded RUPALIT® high-frequency litz wires were used, whose numerous individually enamelled strands significantly reduced AC losses.
- Thermal Relief: Due to the fine structure and optimized effective cross-section, heat losses were reduced, allowing for a more compact transformer design.
- Increased Insulation: To cope with the high electrical stresses, the litz wires were provided with additional film insulation to ensure compliance with normative requirements.
- Simulation & Dimensioning: Using the LiWiCalc® calculation tool, the number of strands, single wire diameter, and stranding patterns were precisely adapted to the customer's operating frequency and thermal constraints.
Result
The newly designed HF litz wire enabled a more compact, thermally more robust transformer with significantly lower losses. The measurement results confirmed a noticeable reduction in AC losses as well as full compliance with the standards – allowing the customer to design its switched-mode power supply more efficiently and reliably while maintaining the same format.
Open industrial switched-mode power supply with transformer and power electronics, exemplary of compact and efficient power supply solutions in industrial electronics.
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