Calculator KB-50
Toroidal Core Turns Calculator
For DC-DC converters and filters: the ring’s AL, inductance, and current are all you need.
Result
In brief: Calculate an inductor on a toroidal core: turns based on AL, actual inductance, flux density and saturation check for ferrite or powdered-iron cores, and wire diameter. Example: Number of turns: 22 t.
Calculation example
| Desired inductance | 47 µH |
|---|---|
| Core AL | 100 nH/t² |
| Peak current | 3 A |
| Core cross-sectional area Ae | 40 mm² |
| Material | Ferrite, up to 0.3 T |
| Number of turns | 22 t |
|---|---|
| Inductance at these turns | 48.4 µH |
| Peak flux density | 0.165 T |
| Of material limit | 55 % |
| Wire diameter at 4 A/mm² | 0.98 mm |
How it is calculated
B = L · I / (N · Ae)
The AL parameter gives the inductance of one turn on this core. The number of turns is rounded up to a whole number, while the flux density shows how much headroom remains before saturation: beyond that point, inductance drops sharply.
What to look for
- With powdered cores, inductance decreases gradually as current rises, and the datasheet includes a graph of this relationship.
- Check painted cores of unknown origin: measure the inductance with 10 turns and calculate AL.
Frequently asked questions
How do you calculate the number of turns on a toroid using AL?
N = √(L / AL). For 47 µH and AL of 100 nH/turn², N is 21.7, so round up to 22 turns for 48.4 µH.
How do you check that the core won't saturate?
B = L · I / (N · Ae). For 48.4 µH, 3 A, 22 turns, and 40 mm², B is 0.165 T: that's within the margin for ferrite with a limit of about 0.3 T.
How does a powdered iron core differ from a ferrite core?
Powdered iron handles flux densities of around 1 T and saturates gradually, but has higher losses at high frequencies. Ferrite is more efficient at high frequencies, but saturates abruptly at around 0.3 T.
