In high-frequency power supply and transformer design, the air gap is often a critical factor. Many engineers ask the same question: Since an air gap helps prevent core saturation, can it also increase transformer power? This article explores the electromagnetic principles behind the air gap and examines both the positive and negative impacts on transformer performance.

How the Air Gap Works

The magnetic permeability of air is about 4π×10⁻⁷ H/m, which is far lower than that of power ferrite materials (μᵣ≈2000–5000). When an air gap is introduced into the magnetic core, the magnetic reluctance (Rₘ) increases significantly. According to Hopkinson’s Law:

Φ=NIRmΦ = \frac{NI}{Rₘ}

An increase in reluctance reduces the magnetic flux (Φ), which in turn decreases flux density (B):

B=ΦAB = \frac{Φ}{A}

When the flux density B remains below the saturation flux density, the core does not saturate, and the inductance remains stable. This explains why a properly designed air gap allows the transformer to handle higher current without premature saturation.

Positive Effects: Preventing Saturation and Storing Energy

• Saturation suppression: By lowering effective permeability, an air gap prevents magnetic core saturation under higher currents.

• Increased energy storage: Especially in inductors and LLC resonant converters, a well-designed air gap improves energy storage and system stability.

Negative Effects: Heating and Reduced Efficiency

However, a larger air gap does not always mean better performance. Excessive air gap introduces several drawbacks:

1. Increased heating: Higher current leads to greater copper losses (P = I⊃2;R), resulting in rapid winding temperature rise.

2. Leakage flux losses: A larger gap causes more leakage flux, which can induce eddy current losses in windings at high frequency.

3. Reduced coupling coefficient: An oversized gap weakens magnetic coupling between primary and secondary, lowering transfer efficiency and reducing secondary voltage output.

In short, while a moderate air gap enhances reliability, an oversized air gap reduces power capability and efficiency.

Balancing Design in Practice

When designing transformers, engineers must carefully balance:

• Operating current vs. core material properties

• Switching frequency vs. winding structure

• Thermal management vs. efficiency targets

• Application scenarios (e.g., high-frequency power supplies, battery chargers, resonant converters)

Typically, the optimal air gap is determined through a combination of material selection, simulation, and prototype testing.

Conclusion

The air gap itself does not directly increase transformer power. Instead, it plays a vital role in preventing saturation and ensuring stable operation. A carefully designed air gap improves transformer performance and reliability, but excessive gap size can reduce output power and increase thermal issues.

At Trafopsu, we specialize in the design and manufacturing of high-frequency transformers and magnetic components. With extensive expertise in air gap optimization and efficient energy transfer, we provide customized solutions for battery chargers, power modules, and resonant converters.

Contact us today to discuss your project and learn how we can support your next-generation power designs.