What Is a PFC Inductor?
A PFC inductor is the key magnetic component in a power factor correction (PFC) stage. It shapes the input current of a power supply to follow the AC line voltage, reducing harmonic distortion and improving power factor in compliance with standards such as IEC 61000-3-2 and ENERGY STAR. PFC inductors are found in every modern switch-mode power supply above roughly 75 W, including server power supplies, telecom rectifiers, EV chargers, LED drivers and industrial converters.
Working Principle of the PFC Stage
The most common PFC topology is the boost converter. The PFC inductor stores energy during the switch-on interval and releases it to the output during switch-off. In CCM (continuous conduction mode) the inductor current never falls to zero, giving low ripple and lower EMI; in CRM/DCM the current returns to zero each cycle, which simplifies the control but raises peak currents. The inductor therefore defines the ripple amplitude, the peak current stress on the switch and diode, and the overall efficiency.
Key Specifications
| Parameter | Typical Range | Why It Matters |
|---|---|---|
| Inductance | 100 µH – 1 mH (1 kW class) | Sets current ripple in CCM boost PFC |
| Saturation current | 1.5 – 3× rated peak current | Prevents inductance collapse under line surge and inrush |
| DC resistance (DCR) | 50 mΩ – 500 mΩ | Dominant copper loss; lower DCR improves efficiency |
| Core loss | Depends on material at 60–200 kHz | Main source of core heating in high-frequency designs |
| Temperature rise | < 50 °C above ambient | Long-term reliability and insulation life |
| Inductance tolerance | ±10% to ±20% | Affects ripple and control-loop stability |
Core Materials for PFC Inductors
Because a boost PFC inductor carries a large DC bias, the core must hold its permeability under DC. The main options are:
- Powder cores (sendust, MPP, high flux, Kool Mμ) – distributed air gap, soft saturation, excellent DC bias performance. Sendust offers a good cost/loss balance; MPP has the lowest loss; high flux the highest saturation flux density.
- Gapped ferrite – very low core loss at moderate frequencies, but the concentrated air gap causes fringing flux and requires careful winding placement; the inductance collapses sharply if the core saturates.
For CCM boost PFC at 60–150 kHz, powder cores are usually preferred because the soft saturation curve tolerates the large DC bias without a hard inductance collapse.
Design and Selection Steps
- Define output power, input voltage range and switching frequency.
- Choose the conduction mode (CCM for >1 kW, CRM/DCM for lower power).
- Calculate the required inductance from the allowed current ripple (typically 20–40% of peak current).
- Check the energy handling requirement (½·L·I²) and select a core size.
- Verify DC bias performance: confirm inductance at the peak operating current does not drop below the ripple requirement.
- Estimate copper and core loss, then verify the temperature rise.
Applications
- Server and telecom power supplies
- EV onboard chargers and charging piles
- LED drivers and lighting power
- Industrial SMPS and motor drive front ends
- UPS and renewable energy inverters
Custom PFC Inductors from Shaanxi SiRui Technology
Shaanxi SiRui Technology Co., Ltd manufactures custom PFC inductors and power inductors using sendust, MPP, high flux and Kool Mμ powder cores as well as gapped ferrite. We tailor inductance, saturation current and DCR to your converter’s exact operating point, and provide engineering samples for rapid validation. Our ISO9001:2015 certified factory delivers RoHS and REACH compliant components verified by SGS and CTI. Contact us with your power specification for a design proposal and quotation.
FAQ
Q: Why does the inductance of my PFC inductor drop under load?
A: Powder cores have distributed gaps and soft saturation; check the DC bias curve and make sure the operating inductance at peak current still meets the ripple budget.
Q: Sendust or MPP core?
A: Sendust is cost-effective with moderate loss; MPP has lower core loss and better thermal stability for high-frequency or high-ripple designs. Choose by loss budget and cost.
Q: How much ripple is acceptable in a boost PFC?
A: A common design target is 20–40% of the peak inductor current. Lower ripple reduces EMI and RMS stress but requires more inductance and a larger core.
Related Articles
- Alloy Powder Cores: Sendust, MPP, High Flux & Kool Mμ Guide
- How to Choose the Right Power Inductor
- SMD Power Inductor: Key Specs & Selection Tips
- EMI Filter Design Guide
Looking for a high-efficiency PFC inductor? Talk to Shaanxi SiRui Technology Co., Ltd for a custom design and free samples.