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Bobbin

On the Bobbin tab you add the non-magnetic, non-conductive parts: bobbins, spacers, insulation and potting. They carry no current, but they conduct heat, set the permittivity for capacitance and give regions where you can refine the mesh. You give each group its material on the Assembly tab.

Use a bobbin body for Why
Heat transfer Heat flows from the windings and the core through the bobbin. Fill air pockets between windings and core with a bobbin body of material Air: without a body there, the pocket faces become external boundaries of the heat model. See Heat.
Capacitance The permittivity of the bobbin material enters the winding capacitance. See Setup and Materials.
Mesh refinement A bobbin body between windings is a region you can refine on the Mesh tab, for more accurate leakage inductance and interwinding capacitance.
Bobbin tab of the Flyback Transformer template with the group Group1bobbin and an angled 3D view of the bobbin alone
Bobbin tab of the Flyback Transformer template, with the bobbin alone in the 3D view. The 3D view is described on 3D View.

Geometry Groups

+ New Group (1) adds a group. Each row is one group: the switch (2) turns it on or off, Configure (3) opens its settings in a new tab, and ⋮ (4) copies or deletes it (as on the Coil tab). A Default bobbin is built again around the core and the coil whenever they change. A bobbin from CAD that overlaps them needs Cut by Other Objects on import (see below).

Group settings

Group settings of Group1bobbin with Source set to Template, Scale in mm and zero translation and rotation
Group1bobbin of the Flyback Transformer: Source Template (5), Import (6), Scale mm (7), Translation and Rotation (8, 9).
Setting Values What it does
Source (5) Template (default), CAD Template: build the bobbin with the Geometry Builder. CAD: import it with Import (6); the dialog and its options are described on Core (Importing from CAD).
Scale (7) µm, mm (default), cm, m, in, ft Length unit of the geometry and of the builder dimensions. Set it before you build or import.
Translation and Rotation (8) mm and deg Moves the group: translation first, then rotation about the x-, y- and z-axes, with absolute values (see Coil). Enter the values and click Apply (9).

Geometry Builder

Choose a Type (10), enter the dimensions (11) in the Scale unit (the letters match the sketch in the Specification panel (12)) and click Apply (13).

Geometry Builder panel with Type Default and the dimensions A, B, R, H, r, h, Gx and Gz of the bobbin
Geometry Builder of Group1bobbin: a round Default bobbin with A = B = 0, R = 7.1 mm and H = 8.5 mm.
Specification panel with the dimension sketch of the Default bobbin, top and side views with the letters A, B, R, H, r, h, Gx and Gz
Specification sketch of the Default bobbin: the letters match the Geometry Builder fields.
Type Builds
Default A bobbin between the core and the winding, round or rectangular, with flanges
Box, Cylinder Basic shapes, for example spacers, insulation sheets and potting blocks

Importing from CAD

One file per group, in STEP or IGES format. The Import CAD dialog works as on the Core tab: click Import (14) and choose the file, check Scale (15), choose the Geometry Handling Algorithm (16) and click Ok (17). A bobbin drawn in CAD often overlaps the coil or the core: import it with Cut by Other Objects, so the overlapping parts are cut away from the bobbin.

Import CAD dialog for a bobbin group with the Geometry Handling Algorithm set to Cut by Other Objects and the imported bobbin of the Flyback Transformer in the 3D view
Import CAD for a bobbin: Import (14), Scale (15), Geometry Handling Algorithm set to Cut by Other Objects (16), Ok (17).