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The LLC resonant converter has become one of the most widely adopted topologies in modern power electronics, especially in high-efficiency and high-power-density applications. At the heart of this topology lies the LLC transformer, a component that directly impacts system performance, energy efficiency, and electromagnetic compatibility. Whether you're designing a power module for servers, industrial systems, or electric vehicle chargers, selecting the right LLC transformer is critical to ensuring long-term reliability and maximum output.
This article will guide you through the essential considerations for choosing an LLC transformer that meets your power supply's requirements, with insights from Trafopsu, a professional provider of magnetic component solutions for resonant power systems.
In an LLC resonant converter, the transformer is not just responsible for energy isolation and transfer. It is an integral part of the resonant circuit and works in harmony with the resonant inductor and capacitor to achieve zero-voltage switching (ZVS). Unlike traditional transformers, the LLC transformer must be carefully designed to include or cooperate with specific leakage inductance, operate efficiently at high switching frequencies, and maintain thermal and electrical stability.
A mismatched transformer in an LLC converter can lead to several critical issues: inefficient power conversion, increased thermal stress, unwanted EMI emissions, and even resonant mismatches that destabilize the system. In contrast, a well-optimized LLC transformer can push system efficiency above 94%, reduce temperature rise, and simplify EMI filtering. The right transformer is essential for compact, reliable, and efficient power designs.
Your choice of transformer begins with defining the power level. For LLC converters, this typically ranges from 200W to 1000W. However, it is important to account for peak load, ambient temperature, and duty cycle. For example, Trafopsu provides LLC transformers optimized for 500W power levels, covering a broader application range from 200W up to 800W. These are ideal for use in server power supplies, industrial power systems, and fast-charging modules.
LLC converters generally operate at switching frequencies between 70kHz and 150kHz. The transformer's magnetic core material must exhibit low losses within this frequency range to ensure high efficiency and reduced heat generation. Materials like DMR95 or PC95 ferrites are commonly used for their favorable magnetic characteristics at high frequencies. Trafopsu incorporates such low-loss materials into their transformer designs to maintain efficiency even under demanding load conditions.
In LLC designs, the leakage inductance of the transformer is not an unwanted byproduct but an essential component of the resonant tank. Therefore, transformer design must provide controlled and consistent leakage inductance—typically between 4 and 10 microhenries—depending on the application. Trafopsu offers integrated transformer designs where the required leakage inductance is built into the structure itself, eliminating the need for external resonant inductors. This not only reduces component count and PCB space but also improves the reliability and integration level of the entire power system.
Core geometry affects many transformer parameters, including leakage characteristics, thermal behavior, and size. The most common core types used in LLC transformer applications are ETD49, PQ50, and RM10. For ultra-compact and high-density designs, planar cores and custom ferrite shapes are also employed. Trafopsu offers both standard and customized core configurations, allowing you to tailor the transformer structure to your specific PCB layout and thermal requirements.
LLC transformers often handle high currents and must dissipate the resulting heat effectively to maintain system stability. Thermal design is influenced by the wire gauge, winding method, core material, and overall structure. Trafopsu optimizes winding layouts and uses high-quality insulation materials to minimize core and copper losses, ensuring low temperature rise and reliable long-term performance even in enclosed or fanless systems.
Transformers operating at high frequencies can introduce significant electromagnetic interference. Careful design strategies such as distributed capacitance optimization, multi-layer shielding, and winding interleaving help mitigate these effects. Trafopsu implements these techniques to deliver magnetic components with excellent EMI performance, helping system integrators meet international EMC compliance requirements.
When selecting an LLC transformer, it is important to ensure that it meets relevant safety and insulation standards, such as UL 60950, IEC 60950, and EN 62368. Trafopsu’s magnetic components comply with global standards, providing reinforced insulation and sufficient creepage/clearance distances for both industrial and consumer-grade power systems.
Depending on your design goals—such as size constraints, modularity, or thermal requirements—LLC transformers can be implemented in several structural forms. Trafopsu supports various formats, including single-core transformers with integrated resonant inductance, dual-core assemblies separating transformer and inductor, and magnetic integrated planar solutions. Each configuration serves specific needs in terms of power density, leakage control, and manufacturability.
Designing a high-performance LLC transformer is a complex process involving simulation, material selection, structural modeling, and prototype testing. Trafopsu provides full technical support to assist clients through every stage of product development. This includes electrical circuit matching, magnetic modeling, thermal simulations, and fast prototyping. Their team also offers assistance with global safety certifications to help accelerate your product’s time-to-market.
Trafopsu specializes in high-frequency magnetic component solutions, particularly for resonant power supply applications. With extensive experience in LLC transformer design, they offer reliable and cost-effective solutions that meet the rigorous demands of modern power electronics. Their transformers feature high efficiency, controllable leakage inductance, compact structures, and compliance with international safety standards.
Whether you need a standard component or a fully customized solution, Trafopsu can provide transformer designs that improve system performance, reduce development time, and ensure stable production quality.
You can explore their full range of magnetic solutions and request technical consultation by visiting their official website at www.trafopsu.com.
Choosing the right LLC transformer is crucial to the success of any resonant power supply design. It impacts everything from efficiency and thermal performance to EMI behavior and long-term reliability. By carefully considering power level, frequency, leakage inductance, thermal design, and core geometry, you can select a transformer that meets both functional and regulatory requirements.
For expert support and high-quality LLC transformer solutions, Trafopsu stands out as a trusted partner for power system developers worldwide. Their deep technical expertise and commitment to quality can help you bring your next-generation power supply project to life with confidence.
