Core loss is one of the most critical calculations in magnetic component design. Too little core loss calculation and your transformer overheats; too conservative and you oversize the core. The Steinmetz equation is the standard empirical model for estimating core loss in ferrite and powder cores.
This guide explains the Steinmetz equation, how to use it, its limitations, and modern improvements like iGSE for non-sinusoidal waveforms.
Shaanxi SiRui Technology Co., Ltd. engineers use core loss modeling in every custom transformer and inductor design. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. The Steinmetz Equation
The classic Steinmetz equation estimates core loss per unit volume:
P_core = k × f^α × B^β
- P_core = power loss per unit volume
- f = frequency (Hz)
- B = peak flux density (T)
- k, α, β = material-specific Steinmetz coefficients
2. Typical Coefficients (Mn-Zn Ferrite)
| Parameter | Typical Value |
|---|---|
| k | 20–50 (unit-dependent) |
| α (frequency exponent) | 1.2–1.5 |
| β (flux exponent) | 2.5–3.0 |
3. Limitations
- Only valid for sinusoidal excitation
- Not accurate for square-wave waveforms (common in SMPS)
- Doesn’t account for DC bias
- Accuracy depends on staying within test range
4. Improved Models
iGSE (improved Generalized Steinmetz Equation): handles non-sinusoidal waveforms by considering dB/dt. More accurate for square-wave drive in forward and flyback converters.
Manufacturer loss curves: for practical design, reading published core loss vs. flux density curves is often faster and more accurate.
5. Total Loss = Core Loss + Copper Loss
P_total = P_core + P_copper. A well-designed transformer has roughly balanced core and copper losses at rated load.
6. Practical Tips
- Always use manufacturer core loss curves, not just Steinmetz
- Account for temperature effects
- Verify with prototype measurement
- Add thermal margin (design for 80% of rated loss)
7. Sirui-Tech Design Capability
Our engineering team uses core loss modeling and thermal analysis in every custom magnetic design, verified with prototype testing before production.
Conclusion
The Steinmetz equation is a useful starting point, but always verify with manufacturer curves and prototype measurement. Balance core loss and copper loss for an optimized design.
Need a custom magnetic design? Contact Sirui-Tech at sales@sirui-tech.com with your application requirements.