Proximity Effect Further Increases Winding Losses

Proximity Effect Inductor

Proximity effect - losses due to eddy current generated by the magnetic field experienced by a particular conductor section but generated by the current flowing in the rest of the winding.

Design methods for minimizing proximity effect losses discussed later.

Minimum Winding Loss

• Pw = Pdc + Pec ; Pec = eddy current loss.

Optimum conductor size

^ Resistance J

• Pw = { Rdc + Rec} [Irms] = Rac [Irms]

• Rac = FR Rdc = [1 + Rec/Rdc] Rdc

\ / Rec

• Minimum winding loss at optimum conductor size.

• Pw = 15 Pdc

• Pec = 05 Pdc

dopt» d d = conductor diameter or thickness

• High frequencies require small conductor sizes minimize loss.

• Pdc kept small by putting may small-size conductors in parallel using Litz wire or thin but wide foil conductors.

Magnetics - 19 WPR - 1/'02

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