# Core Materials # Core Materials & Properties The core material of an inductor dramatically affects its performance. Choosing the right core is essential for achieving the desired inductance, Q factor, and frequency response in VIC applications. ## Why Use a Core? A magnetic core increases inductance by providing a low-reluctance path for magnetic flux: L = μ₀μᵣN²A/l The relative permeability (μᵣ) of the core multiplies the inductance compared to an air core. ## Core Material Comparison
Materialμᵣ (typical)Frequency RangeSaturationCost
Air1AnyN/AFree
Iron Powder10-1001 kHz - 100 MHzHigh (0.5-1.5T)Low
Ferrite (MnZn)1000-100001 kHz - 1 MHzLow (0.3-0.5T)Medium
Ferrite (NiZn)50-1500100 kHz - 500 MHzLow (0.3-0.4T)Medium
Laminated Silicon Steel2000-600050 Hz - 10 kHzHigh (1.5-2.0T)Low
Amorphous Metal10000-10000050 Hz - 100 kHzHigh (1.5T)High
Nanocrystalline15000-1000001 kHz - 1 MHzHigh (1.2T)High
## Core Losses All magnetic cores dissipate energy through two mechanisms: ### 1. Hysteresis Loss Energy lost each time the core is magnetized and demagnetized. Ph ∝ f × Bmaxn (n ≈ 1.6-2.5) Proportional to frequency and flux density. ### 2. Eddy Current Loss Circulating currents induced in the core material. Pe ∝ f² × Bmax² Proportional to frequency squared - dominates at high frequencies. ### Steinmetz Equation Pcore = k × fα × Bβ × Volume Where k, α, β are material-specific constants from datasheets. ## Ferrite Materials for VIC Ferrites are the most common choice for VIC frequencies (1-50 kHz):
MaterialμᵢOptimal FrequencyApplication
3C90 (TDK)230025-200 kHzPower transformers
N87 (EPCOS)220025-500 kHzGeneral purpose
N97 (EPCOS)230025-150 kHzLow loss
3F3 (Ferroxcube)2000100-500 kHzHigher frequency
77 Material (Fair-Rite)2000Up to 1 MHzEMI/RFI suppression
## Iron Powder Cores Micrometals and Amidon iron powder cores are popular for their: - High saturation flux density - Gradual saturation (soft saturation) - Good temperature stability - Self-gapping (distributed gap) ### Common Iron Powder Mixes
MixμColorFrequency Range
Mix 2675Yellow/WhiteDC - 1 MHz
Mix 5275Green/BlueDC - 3 MHz
Mix 210Red/Clear1 - 30 MHz
Mix 68Yellow10 - 50 MHz
## Core Shapes #### Toroidal Doughnut shape with closed magnetic path. Excellent flux containment, low EMI. Harder to wind but very efficient. #### E-Core / EI-Core E-shaped halves that mate together. Easy to wind on bobbin. Can add air gap easily. #### Pot Core Cylindrical with center post. Shields winding from external fields. Good for sensitive applications. #### Rod Core Simple cylindrical rod. Open magnetic path, lower inductance per turn but no saturation issues. ## Core Saturation When the magnetic flux density exceeds the saturation limit: - Permeability drops dramatically - Inductance decreases - Current increases rapidly - Core heating increases #### Avoiding Saturation: Bpeak = (L × Ipeak) / (N × Ae) < Bsat Always check that peak flux density stays below saturation limit of your core material. ## Recommendations for VIC
Frequency RangeRecommended CoreNotes
1-10 kHzN97/3C90 ferrite or iron powderLow loss at these frequencies
10-50 kHzN87/3F3 ferriteGood balance of μ and loss
50-200 kHz3F3/3F4 ferrite or Mix 26 powderLower permeability, lower loss
>200 kHzNiZn ferrite or Mix 2 powderDesigned for high frequency
**VIC Matrix Calculator:** The Choke Design module includes a core database with AL values and frequency recommendations. Select your core and it will calculate the required turns for your target inductance. *Next: Wire Gauge & Material Selection →*