4kW High-Power SMPS Design and LLC Transformer Challenges with Levane Power Product Practice

Designing industrial‑grade high‑power switching power supplies – especially the critical transformer section – has always been a high‑ground challenge in power electronics. Whether used for onboard DC‑DC converters, tethered drone power systems, or industrial equipment electrification, the quality of transformer design directly affects the efficiency, stability, and reliability of the entire system. For the 4kW power level, LLC transformer design is particularly challenging.

I. Three Major Challenges in 4kW Power Supply LLC Transformer Design

1. Challenge 1: Insulation and Safety under High Voltage

4kW usually corresponds to output voltages of several hundred volts or even higher. High output voltage means that the primary and secondary windings must withstand extreme insulation stress. Poor insulation handling will cause partial discharge and, in severe cases, equipment breakdown or destruction. This requires the winding structure to increase interlayer insulation thickness, use triple‑insulated wire, ensure a creepage distance ≥14 mm, and meet reinforced insulation requirements (Class F/H). Vacuum impregnation must also be used to remove any micro‑bubbles inside the winding, eliminating the risk of partial discharge.

2. Challenge 2: Thermal Management and Losses under High Current

The 4kW operating condition implies considerable current on both primary and secondary sides. The high current flowing through the windings generates significant copper losses (winding losses), while the magnetic core simultaneously produces core losses at high switching frequencies. If the heat generated by copper and core losses is not properly conducted away through an appropriate thermal structure, system efficiency and stability will be severely affected. To counteract skin and proximity effects, the windings must use multi‑strand Litz wire to reduce high‑frequency losses, and forced air cooling or liquid cooling is required for overall thermal management. At the 4kW power level, forced air cooling is the minimum requirement, and the temperature rise must be strictly controlled within 85°C.

3. Challenge 3: Co‑optimisation of High Voltage and High Power

The coexistence of high voltage and high current creates a “seesaw” effect in transformer design. To achieve insulation, the creepage distance must be increased; for heat dissipation, the metal surface area and volume must be enlarged. However, the new energy market constantly demands higher power density – delivering extremely high power in a very small space. How to achieve high power density while ensuring reliable insulation is a core difficulty that must be overcome in 4kW‑level LLC transformer design.

II. Core Design Concepts for a 4kW LLC Transformer

1. Topology Choice: Why LLC?

In 4kW‑level high‑power applications, the full‑bridge LLC topology is currently a mainstream and mature choice because it can achieve ZVS (zero‑voltage switching) of the primary switches and ZCS (zero‑current switching) of the secondary rectifiers over a wide load range, resulting in very low switching losses and electromagnetic interference. Compared to a phase‑shifted full bridge, the full‑bridge LLC is particularly suitable for applications with a fixed input voltage and adjustable output voltage. Moreover, its gain curve can be flexibly adjusted, allowing operation in the frequency range of 60–150 kHz, typically around 100 kHz.

2. Core Material Selection: Nanocrystalline vs. Ferrite

Core selection is a key step for the 4kW power level. The mainstream options are:

• High‑power‑density route – nanocrystalline cores (e.g., FeCuNbSiB) are recommended. They have a saturation flux density as high as 1.2 T (far exceeding ferrite’s 0.39 T) and extremely low high‑frequency losses, enabling the same power output in a much smaller volume. They also demand higher insulation resistance (≥10¹² Ω·cm) and temperature stability (Curie temperature ≥200°C).

• Cost‑effective route – two EE65 or EE85 ferrite cores can be used in parallel. A single EE85B core can handle approximately 2.5 kW; two in parallel meet the 4kW requirement. For ferrite, low‑loss grades such as PC95 or 3F46 are recommended.

3. Winding Design and Turns Ratio Calculation

The gain of an LLC transformer varies with load (Q) and normalised frequency (fₙ); it is not fixed. The design must ensure that, at the minimum input voltage, the system still provides sufficient gain to stabilise the output voltage.

• Turns ratio n (estimate) – assuming unity gain at the resonant frequency, n = V_in / V_o provides a starting point.

• Primary turns N_p – N_p = V_in / (4·fₛ·B_m·Aₑ), where B_m is typically 0.12–0.15 T.

• High‑voltage winding insulation – use a segmented multi‑layer winding to reduce interlayer voltage stress; use triple‑insulated wire (TIW) to increase withstand voltage (TIW rated up to 1250 Vpk).

• High‑power structure – primary dual‑windings in series, secondary multiple windings in parallel effectively reduce insulation stress and increase power density.

4. Thermal Design Strategy

Thermal management under full 4kW load is critical for engineering implementation:

• Copper losses – the skin depth limits the conductor diameter; high current must use multi‑strand Litz wire.

• Core losses – choose low‑loss ferrites like PC95 (P_v ≈ 300 mW/cm³ at 100 kHz / 0.2 T) or nanocrystalline (≈120 mW/cm³ at 500 kHz).

• Cooling – forced air cooling is the minimum; liquid cooling may be considered when necessary.

• Safety margin – reserve at least 20% power margin to ensure reliable continuous operation.

III. Analysis of Levane Power’s 4kW Airborne Power Supply Product

Levane Power Technology Co., Ltd. focuses on high‑power DC‑DC power solutions. By examining its HLF4K series lightweight airborne DC‑DC power supply, we can see the design concepts at the 4kW power level.

1. Product Positioning and Applications

The HLF4K series is designed for demanding applications such as drones, tethered drones, and industrial equipment electrification. The product family covers a complete power matrix from 3 kW to 120 kW, with the HLF4K as the core node for the 4kW level. This series is widely used in emergency communications, emergency lighting, disaster relief, and other complex scenarios that require long‑endurance power solutions. It maintains stable, high‑power operation even under the stringent requirements of long flight duration and high reliability.

2. Key Performance Specifications

The HLF4K series supports an ultra‑wide input voltage range from 600 VDC to 1600 VDC – a highly forward‑looking design concept. Such a wide input range demands that the control strategy and gain curve of the LLC converter accommodate a very large variation. Regarding output voltage platforms, the product can be configured with multiple voltage options, demonstrating modularity and platformisation. In terms of efficiency, Levane Power achieves ≥96% or even 98% in related products, illustrating its expertise in LLC topology, low‑loss magnetic cores, and low‑RDS(on) switches.

3. Reliability Design

For a 4kW high‑voltage, high‑power device, reliability is the key difference between a commercial product and a laboratory prototype. Levane Power implements a complete automotive‑grade test system for each product, strictly performing component stress analysis, thermal cycling, vibration shock, damp heat, safety compliance, EMC tests, and other full‑type tests. In addition, MTBF analysis, FMEA, accelerated ageing, and HALT are introduced as reliability validation methods. These measures are the fundamental guarantee that the series can operate stably at industrial temperature ranges (−40°C to +85°C).

4. Design and Market Philosophy

By reviewing the design philosophy and market strategy of Levane Power’s HLF4K series, one can see their investment and accumulation in 4kW‑level LLC converter design:

• Wide‑voltage adaptability – the 600 V‑1600 V range supports voltage standard differences across countries and regions.

• High power density – a core competitive metric for lightweight airborne DC‑DC applications.

• Customisation services – deep customisation including ±10% voltage/current adjustment, CAN/RS485 communication interfaces, etc.

• Lifecycle reliability – end‑to‑end quality control from design through production to testing.

IV. Conclusion

Designing a 4kW high‑power LLC transformer is a systematic engineering task that tests comprehensive power electronics knowledge. Every step – from core material selection, winding structure and insulation handling, to thermal management and reliability verification – affects the performance and stability of the final product.

From the analysis of Levane Power’s HLF4K series lightweight airborne DC‑DC power supply, we can see that an excellent 4kW‑class high‑power supply requires not only deep technical expertise but also simultaneous efforts in wide‑voltage compatibility, high power density, platform scalability, and high reliability. With more than twenty years of accumulated experience in onboard DC‑DC converters, tethered drone power systems, and industrial equipment electrification, Levane Power is able to provide complete solutions ranging from 1 kW to 120 kW for customers across different industries.

For industrial users evaluating a 4kW‑class high‑power supply, we recommend focusing on the following five dimensions:

• Whether the transformer insulation and creepage distance design meet the standards;

• Whether the thermal management system can handle the heat dissipation requirements under full 4kW load;

• Whether an automotive‑grade reliability verification system is in place;

• Whether wide‑voltage input and output voltage platform customisation are available;

• Whether the power platform is scalable to 6kW/8kW/12kW.

With solid technical accumulation and an innovation‑driven spirit, Levane Power continues to inject strong momentum into the global power and energy industry, empowering high‑quality development in both industrial and aviation fields.