Transformer Core & Magnetic Circuit Designer

Assumes sinusoidal excitation: the required-turns formula (V_rms = 4.44·f·N·B·A_e) is Faraday's law for a sine wave specifically. A square or pulse waveform — as in most switch-mode converters — has a different volt-second relationship (a bipolar square wave uses a factor of 4, not 4.44) and will need re-deriving from ∆B = (1/NA)∫v(t)dt rather than read off this tool directly. This also isn't a full inductor design flow: a DC-biased or gapped inductor is more naturally specified by target inductance and DC/peak current than by an RMS voltage, though the same reluctance network and saturation check underneath still apply once you know the ampere-turns.

How this is built: a magnetic circuit solved exactly like an electrical one — reluctance in place of resistance, flux in place of current, magnetomotive force in place of voltage. Required turns come from Faraday's law above, rounded up to the nearest whole turn, which is why the actual peak flux density is always at or slightly under your target, never over. Series paths add reluctance directly; the gap and an optional shunt/concentrator combine as a parallel pair — including the zero-gap edge case, where the near-zero-reluctance main path correctly takes all the flux and the shunt takes none, rather than the reverse. The shunt is checked against its own saturation rating independently of the main core's, since a small, high-permeability shunt carrying most of the flux commonly reaches a far higher flux density than the core it's attached to ever does. The air gap includes a standard first-order fringing correction — flux bulges outward at the gap, enlarging its effective area beyond the core's own cross-section, so the gap's reluctance (and the "effective area" row below) is a little lower than a naive same-area calculation would give. That correction is only reliable for a gap that's small relative to the core's own cross-sectional width — a warning appears if your gap is large enough that this stops holding. Magnetizing current is treated as sinusoidal, valid well below saturation; real magnetizing current distorts as a core approaches Bsat. Core losses (hysteresis and eddy current) are not modeled at all — at higher frequencies, usable flux density is often limited by heating well before Bsat, so check the material's loss curves separately. This is the analytical starting point real designs use before refining the geometry in a field solver (COMSOL, ANSYS Maxwell, etc.) — not a replacement for one.