Nanocrystalline Common Mode Choke Cores for EMI Filters
CenturaCores CMC series are nanocrystalline common mode choke cores designed for high‑performance EMI suppression in solar inverters, EV chargers, industrial drives, and switched‑mode power supplies. These cores provide very high permeability, stable inductance over a wide frequency range, and low core losses, allowing designers to meet stringent EMC standards in compact footprints.
What is a common mode choke core?
A common mode choke core is a magnetic core used with bifilar or multi‑wire windings to block common‑mode noise while passing the desired differential current. In a typical EMI filter, both line conductors are wound on the same core so that normal load current cancels and only common‑mode interference sees high impedance.
Nanocrystalline material provides much higher initial permeability and saturation flux density compared with ferrite, which enables higher impedance at lower turns counts and better performance at elevated temperatures.
Why choose nanocrystalline CMC cores?
Very High Initial Permeability
High common‑mode impedance with fewer turns, reducing copper loss and winding size.
High Saturation & Low Loss
Stable performance under high line currents and wide temperature range.
Wide Frequency Range
Supporting EMI suppression from tens of kilohertz into the low MHz region.
Compact Form Factors
PBT Class B casing to simplify mounting, insulation, and creepage/clearance management on the PCB.
CMC Series Overview
Complete range of nanocrystalline common mode choke cores
| Core Code | Bare Core Size (mm) | Cased Size (mm) | Material | μi (typ) | AL (nH/N²) | Typical Line Current | Notes / Main Use |
|---|---|---|---|---|---|---|---|
| CC-NC-CMC-001-20 | 20×12×8 | 22.6×10.6×10 | Nanocrystalline | 80k-90k | Min 80k μi, AL=>60 | 5-15A | SMPS, small drives |
| CC-NC-CMC-002-25 | 25×16×10 | 27.5×13.8×12.6 | Nanocrystalline | 80k-90k | Min 80k μi, AL=>65 | 5-15A | SMPS, small drives |
| CC-NC-CMC-003-30A | 30×18×10 | 33×16.4×13.2 | Nanocrystalline | 80k-90k | Min 90k μi, AL=>59 | 10-30A | Industrial drives, EV chargers |
| CC-NC-CMC-004-30B | 30×20×15 | 33.6×17.7×17.8 | Nanocrystalline | 80k-90k | Min 90k μi, AL=>88 | 10-30A | Industrial drives, EV chargers |
| CC-NC-CMC-005-40 | 40×25×15 | 44.2×21.6×18.9 | Nanocrystalline | 80k-90k | Min 90k μi, AL=>100 | 30-80A | Solar inverters, high volume |
| CC-NC-CMC-006-40L | 40×32×15 | 43×29×18.8 | Nanocrystalline | 80k-90k | Min 90k μi, AL=>47 | 30-80A | Industrial drives, EV chargers |
Typical Applications
Solar Inverters
AC and DC side EMI filters where designers must meet CISPR / EN55011/22 limits with limited board space.
EV Chargers
On‑board and off‑board EV chargers requiring efficient suppression of common‑mode noise on high current AC or DC lines.
Industrial Drives
Variable frequency drives and industrial motor drives, reducing conducted emissions on input and output lines.
Power Supplies
Switched‑mode power supplies, UPS, and other power conversion equipment with strict EMC requirements.
Design and Selection Guidelines
When selecting a CMC series core, engineers typically start from:
- Line current and maximum operating temperature
- Required common‑mode impedance (or insertion loss) over the relevant frequency band
- Available PCB area and height
- Required safety insulation, creepage, and clearance distances
For a given core size and AL value, the approximate common‑mode inductance can be estimated as L = AL × N², where L is in nH, AL is the core's inductance factor in nH/turn², and N is the number of turns. Larger cores with higher AL values support higher inductance at the same turns but have higher cost and footprint.
You can provide CenturaCores with:
- Line voltage and current (continuous and peak)
- Target attenuation or EMI standard (e.g., CISPR 22 Class B)
- Target frequency range (e.g., 150 kHz–30 MHz)
- Board space and maximum allowable temperature rise
Using this information, a recommended core code, turns, and wire size can be proposed for your common mode choke.
Mechanical and Material Features
Each CMC core is supplied in a black PBT Class B casing with approximately 0.7 mm wall thickness, providing mechanical protection, basic insulation, and consistent thermal behavior under continuous operation. The casing simplifies assembly because the core can be mounted directly to the PCB or into a plastic holder without additional tape wrapping.
Nanocrystalline strip cores are manufactured with tight dimensional tolerances and are resin‑impregnated to minimize vibration and acoustic noise under high magnetic flux swings. This construction improves long‑term stability of AL value and inductance, even under cyclic thermal loading.
Frequently Asked Questions
How do I choose the right common mode choke core for my design?
Start from line current, required attenuation band, and available PCB space, then select a core size and AL value that provides the needed inductance without saturation or excessive temperature rise. CenturaCores can recommend a core and turns when you share your electrical and mechanical constraints.
Can these nanocrystalline CMC cores replace ferrite cores?
In many EMI filter designs, nanocrystalline cores can replace ferrites with fewer turns and better performance at higher currents and temperatures, but the final choice depends on required impedance and cost targets.
What temperature ratings do the CMC cores support?
The nanocrystalline core material and PBT Class B casing are typically suitable for operation up to around 130 °C insulation class, subject to your specific design, creepage distances, and safety approvals.
Do you offer custom core sizes or pre‑wound common mode chokes?
Yes, we offer custom strip width/OD/ID dimensions, custom casing options, and can supply wound and impregnated CM chokes on request for volume applications.
Can the same core be used on the AC and DC side of an inverter?
Often yes, provided the inductance, current rating, and saturation margin are sufficient for each position; many designers standardize on a small set of core sizes across multiple filter stages.
Need CMC Core Design Support?
Share your line current, target attenuation, frequency range, and board constraints. We'll recommend the optimal core size, turns, and wire gauge for your common mode choke design.