Wire Gauge Tables
Appendix C: Core Specifications
Reference specifications for magnetic cores commonly used in VIC choke design. Includes ferrite toroids, iron powder cores, and E-cores.
Core Material Overview
| Material Type | μᵣ Range | Frequency Range | Best For |
|---|---|---|---|
| MnZn Ferrite | 800-10,000 | 1 kHz - 2 MHz | High L, moderate f |
| NiZn Ferrite | 15-1,500 | 500 kHz - 100 MHz | High frequency |
| Iron Powder | 8-100 | 10 kHz - 10 MHz | High current, low cost |
| MPP (Molypermalloy) | 14-550 | DC - 1 MHz | Low loss, stable |
| Kool Mµ | 26-125 | DC - 500 kHz | High current, moderate loss |
| Air Core | 1 | Any | No saturation, linear |
Common Ferrite Materials
MnZn Ferrite Materials
| Material | μᵢ | Bsat (mT) | Frequency | Notes |
|---|---|---|---|---|
| Fair-Rite 77 | 2000 | 480 | <1 MHz | General purpose, high μ |
| Fair-Rite 78 | 2300 | 480 | <500 kHz | Very high μ |
| TDK N87 | 2200 | 490 | <500 kHz | Popular, low loss |
| TDK N97 | 2300 | 410 | <300 kHz | Very low loss |
| Ferroxcube 3C90 | 2300 | 470 | <200 kHz | Low loss at high B |
| Ferroxcube 3F3 | 2000 | 440 | <500 kHz | Higher frequency |
Iron Powder Core Mix Chart
Iron powder cores (Micrometals/Amidon) are identified by color code:
| Mix | Color | μᵣ | Frequency Range | Application |
|---|---|---|---|---|
| -26 | Yellow/White | 75 | DC - 1 MHz | EMI/RFI filters |
| -2 | Red/Clear | 10 | 250 kHz - 10 MHz | RF, resonant circuits |
| -6 | Yellow/Clear | 8.5 | 3 - 40 MHz | Higher frequency |
| -1 | Blue/Clear | 20 | 500 kHz - 5 MHz | Medium frequency |
| -3 | Gray/Clear | 35 | 50 kHz - 500 kHz | Medium μ, low f |
| -52 | Green/Blue | 75 | DC - 200 kHz | High μ, DC bias |
Common Toroid Sizes
FT (Ferrite Toroid) Series
| Size | OD (mm) | ID (mm) | H (mm) | Aₗ (77 mat) | Aₗ (43 mat) |
|---|---|---|---|---|---|
| FT-37 | 9.5 | 4.7 | 3.2 | 884 | 440 |
| FT-50 | 12.7 | 7.1 | 4.8 | 1140 | 570 |
| FT-82 | 21.0 | 13.0 | 6.4 | 2170 | 557 |
| FT-114 | 29.0 | 19.0 | 7.5 | 2640 | 603 |
| FT-140 | 35.5 | 23.0 | 12.7 | 3170 | 885 |
| FT-240 | 61.0 | 35.5 | 12.7 | 4820 | 1075 |
Aₗ values in nH/turn². Highlighted sizes are commonly used for VIC chokes.
T (Iron Powder Toroid) Series
| Size | OD (mm) | ID (mm) | H (mm) | Aₗ (-2 mix) | Aₗ (-26 mix) |
|---|---|---|---|---|---|
| T-37 | 9.5 | 4.9 | 3.2 | 4.0 | 27 |
| T-50 | 12.7 | 7.7 | 4.8 | 4.9 | 33 |
| T-68 | 17.5 | 9.4 | 4.8 | 5.7 | 38 |
| T-80 | 20.2 | 12.6 | 6.4 | 8.5 | 55 |
| T-94 | 24.0 | 14.5 | 7.9 | 8.4 | 70 |
| T-106 | 26.9 | 14.0 | 11.1 | 13.5 | 90 |
| T-130 | 33.0 | 19.7 | 11.1 | 11.0 | 96 |
| T-200 | 50.8 | 31.8 | 14.0 | 12.0 | 120 |
Inductance Calculations
Using Aₗ Value:
L (nH) = Aₗ × N²
N = √(L / Aₗ)
Example:
- Want L = 10 mH = 10,000,000 nH
- Using FT-240-77 (Aₗ = 4820 nH/turn²)
- N = √(10,000,000 / 4820) = 45.6 turns
- Use 46 turns for L ≈ 10.2 mH
Saturation Considerations
Saturation Flux Density (Bsat):
| Material Type | Bsat (mT) |
|---|---|
| MnZn Ferrite | 400-500 |
| NiZn Ferrite | 250-350 |
| Iron Powder | 800-1000 |
| MPP | 750 |
Calculating Peak Flux:
B = (V × t) / (N × Ae)
Where Ae is effective core area. Keep B < 0.5 × Bsat for linear operation.
Temperature Effects
| Material | Curie Temp (°C) | Max Operating (°C) | μ vs. Temp |
|---|---|---|---|
| MnZn Ferrite | 200-250 | 100-120 | Peaks near 80°C, then drops |
| NiZn Ferrite | 300-500 | 150 | Relatively stable |
| Iron Powder | 770 (iron) | 125 (coating limited) | Stable |
Core Selection Guide for VIC
For Primary Choke (L1):
- Moderate L (1-50 mH typical)
- Moderate current handling
- Consider: FT-82-77, FT-114-77, T-106-26
For Secondary Choke (L2):
- May need higher L (10-100 mH) for high Q
- Lower current typically
- Consider: FT-140-77, FT-240-77
For High Frequency (>100 kHz):
- Use lower-μ materials to maintain SRF margin
- Consider: Iron powder -2 or -6 mix, NiZn ferrite
Quick Reference: Turns Calculation
| Desired L | FT-82-77 | FT-240-77 | T-106-26 |
|---|---|---|---|
| 1 mH | 21 turns | 14 turns | 105 turns |
| 5 mH | 48 turns | 32 turns | 236 turns |
| 10 mH | 68 turns | 46 turns | 333 turns |
| 25 mH | 107 turns | 72 turns | 527 turns |
| 50 mH | 152 turns | 102 turns | 745 turns |
Approximate values. Verify with actual Aₗ from manufacturer datasheet.