The power factor correction (PFC) inductor is the largest magnetic component in active PFC circuits found in LED drivers, server power supplies, EV chargers and industrial equipment. Getting the PFC inductor right determines whether the system meets harmonic standards (IEC 61000-3-2) and runs efficiently.
This guide covers boost PFC inductor operation, core material selection, key design parameters, and common topologies.
Shaanxi SiRui Technology Co., Ltd. manufactures PFC inductors in toroidal, drum-core and planar configurations for 100 W to 10 kW applications. Contact: sales@sirui-tech.com | Web: www.sirui-tech.com
1. Why PFC Inductors Matter
Without PFC, input current pulses only near the AC line peaks, drawing high harmonic content. Active PFC shapes input current to follow the sinusoidal voltage waveform, achieving power factor >0.99. The boost inductor is the energy storage element that makes this possible.
2. Core Materials
Powder cores are the most common choice for PFC. Sendust (Fe-Si-Al) offers low loss and stable DC-bias performance. Kool Mμ is similar. High Flux (Fe-Ni) has higher Bsat (1.5 T) for high-current / small-size designs. MPP is the premium option. Powder cores have distributed air gaps, minimizing fringing loss.
Gapped ferrite is lower cost but larger and has higher fringing loss. Nanocrystalline delivers smallest size and highest efficiency for high-end server and EV PFC stages.
3. Key Parameters
- Inductance: 100 μH to 10 mH depending on power
- Peak current: handle peak line current plus current limit without saturation
- Ripple current: typically 10–30% of rated current
- Switching frequency: CCM PFC 50–100 kHz; CRM variable 30–300 kHz
4. PFC Topologies
| Topology | Inductor Type | Best For |
|---|---|---|
| Continuous CCM | Boost, gapped ferrite/powder | >500 W industrial |
| Critical CRM | Smaller powder core | 100–500 W adapters |
| Totem-pole | High-frequency, GaN | EV chargers, server PSU |
| Interleaved CCM | Two smaller inductors | >1 kW high power |
5. Common Mistakes
- Inductance collapses under DC bias—always use DC-bias curve, not initial permeability
- Core saturates at peak current—size for peak, not RMS
- Too much ripple causes EMI and switching loss
- Ignoring temperature rise—PFC inductors run hot
6. Sirui-Tech PFC Capabilities
- Toroidal PFC inductors: powder core, 100 W to 3 kW
- Drum-core PFC: low-cost through-hole
- Nanocrystalline PFC: high-efficiency EV/server
- Custom designs: wound to customer specs
Conclusion
The PFC inductor is the heart of active power factor correction. Powder cores (Sendust, Kool Mμ, High Flux) are standard for CCM PFC. Nanocrystalline serves premium high-efficiency applications. Always verify inductance under DC bias and peak current saturation.
Need a PFC inductor? Contact Sirui-Tech at sales@sirui-tech.com with your output power, input voltage range and switching frequency.