Eddy Current Losses in Transformer Windings and Circuit Wiring

Skin Effect Figure 1 shows the magnetic field (flux lines) in and around a conductor carrying dc or low frequency current I. The field is radially symmetrical, as shown, only if the return current with its associated field is at a great distance. At low frequency, the energy in the magnetic field is trivial compared to the energy loss in the resistance of the wire. Hence the current Introduction As switching power supply operating frequencies increase, eddy current losses and parasitic inductances can greatly impair circuit performance. These high frequency effects are caused by the magnetic field resulting from current flow in transformer windings and circuit wiring. This paper is intended to provide insight into these phenomena so that improved high frequency. performance can be achieved. Among other things, it explains (I) why eddy current losses increase so dramatically with more winding layers, (2) why parallelling thin strips doesn't work, (3) how passive conductors (Faraday shields and C. T .windings) have high losses, and (4) why increasing conductor surface area will actually worsen losses and parasitic inductance if the configuration is not correct.