How to choose magnetic cores and design high-frequency transformers for EV chargers, solar inverters, industrial power supplies and DC-DC converters
Introduction
The high-frequency transformer is the heart of every isolated power converter. Whether you’re designing a 3 kW EV on-board charger, a 100 kW solar string inverter, or a 48V server bus converter, the transformer determines efficiency, power density, and reliability.
In this guide, we break down high-frequency transformer fundamentals, compare core materials, review common topologies, and walk through a practical design workflow.
Shaanxi SiRui Technology Co., Ltd. supplies magnetic cores and custom transformer solutions for high-frequency power conversion.
1. Why High Frequency Matters
For a given power level, increasing switching frequency allows you to shrink the transformer and filter components. But higher frequency also means more core loss and harder cooling. The optimal frequency depends on your core material and application.
2. Magnetic Core Materials for High-Frequency Transformers
Mn-Zn Ferrite (Most Common)
- Saturation flux density: ~0.4–0.5 T
- Best for: 50 kHz – 500 kHz, 100W – 10kW
- Low cost, mature supply chain, wide shape variety
- Limitations: low Bsat → larger core for high power
Nanocrystalline Cores
- Saturation flux density: ~1.2 T (3x ferrite)
- Best for: 20 kHz – 200 kHz, high-density applications
- EV OBC, solar inverters, industrial converters
- Smaller core volume, low loss, excellent temperature stability
Amorphous Cores
- Saturation flux density: ~1.5 T
- Best for: 5 kHz – 50 kHz, UPS, wind converters
Material Comparison Summary
| Parameter | Ferrite | Nanocrystalline | Amorphous |
|---|---|---|---|
| Bsat | 0.4–0.5 T | ~1.2 T | ~1.5 T |
| Frequency Range | 50k–500k Hz | 20k–200k Hz | 5k–50k Hz |
| Core Cost | Lowest | Highest | Medium |
| Best Application | Consumer, Industrial | EV, Solar, High Density | UPS, Wind |
3. Common Transformer Topologies
- LLC Resonant: ZVS, high efficiency, compact. Most popular for EV OBC and server power.
- Phase-Shifted Full-Bridge: Good for medium-to-high power industrial converters.
- Push-Pull / Half-Bridge: Simpler control, lower cost, but harder soft-switching.
4. Application Deep Dives
EV On-Board Charger (OBC)
- 3.6 kW – 22 kW, 100 kHz – 200 kHz
- Mid-range: ferrite PQ cores. Premium: nanocrystalline toroids for higher density.
Solar Inverters
- 50 kW – 350 kW string inverters, 10 kHz – 50 kHz
- Amorphous or silicon steel for lower frequency; nanocrystalline for higher frequency designs.
Server / Telecom Bus Converters
- 1 kW – 6 kW, 200 kHz – 500 kHz
- Ferrite EFD/ER low-profile shapes, very high efficiency (>97%)
5. Practical Design Workflow
- Define requirements: Voltage range, power, frequency, efficiency target, isolation rating
- Select core material & size: Area product method, match material to frequency
- Calculate turns: Primary turns for Bmax, turns ratio for voltage
- Windings design: Litz wire for high freq, minimize leakage and proximity effect
- Verify losses: Core loss + copper loss, check thermal rise
- Prototype & test: Measure efficiency, regulation, temperature rise
6. Common Design Mistakes
- Pushing flux density too high → excessive core loss
- Ignoring inter-winding capacitance → EMI issues
- Underestimating isolation requirements → safety test failures
- Not accounting for temperature rise → thermal runaway
7. Custom Transformer Cores from SiRui-Tech
At Shaanxi SiRui Technology Co., Ltd., we supply Mn-Zn ferrite cores (EE, EI, PQ, ER, ETD shapes), nanocrystalline toroidal cores, amorphous cores, cut cores, and custom coated cores for high-frequency transformer applications.
Conclusion
Designing a high-frequency transformer is a systems problem. The magnetic core material is the foundation—choose wrong, and no amount of winding optimization will save you. As power electronics push toward higher frequency and higher density, nanocrystalline cores are increasingly replacing ferrite in premium applications.
Whether you need standard ferrite cores, custom nanocrystalline toroids, or engineering support for your transformer program, Shaanxi SiRui Technology Co., Ltd. is ready to help.