A Review and Comparison of Solid, Multi-Strands and Litz Style PCB Winding

Abstract

At high frequency, AC resistance of a printed circuit board (PCB) winding becomes important and accounts for a large proportion of planar transformer losses. The winding is then influenced by both skin and proximity phenomenon, which makes the current distribution uneven resulting in an increased resistance. The study of improving AC resistance of a PCB winding has been tackled by many researchers. However, the lack of an overview and comparison among improvements has made it difficult to apply those methods to a specific winding. To overcome the above limitations, this paper investigates the pros and cons of three popular AC resistance optimizing methods: optimizing track width of a solid PCB winding, using multi-strands and using Litz style PCB winding. To verify the theoretical analysis, a total of 12 PCBs are simulated by finite element (FEM) and tested in the laboratory. Five criteria are analyzed, including skin resistance, proximity resistance, AC to DC ratio, total AC resistance and complexity are taken into consideration. The results of this study show that optimizing track width method has a significant improvement on AC resistance while the use of Litz PCB is effective for applications that need stable AC resistance in a wide frequency range. The use of parallel strands winding should be carefully considered as there is not significant benefit in both reducing the AC resistance and AC to DC ratio.

Design of Interleaved Winding for Multilayer Planar Inductor and Its Application in Reducing Current Ringing of LLC Resonant Converter

“…According to the definition of parasitic capacitance of multilayer conductors, the parasitic capacitance value of the planar inductor depends on the interlayer energy and the input voltage. The calculation formula is shown in Equation (11). According to the definition of parasitic capacitance of multilayer conductors, the parasitic capacitance value of the planar inductor depends on the interlayer energy and the input voltage.…”

“…According to the definition of parasitic capacitance of multilayer conductors, the parasitic capacitance value of the planar inductor depends on the interlayer energy and the input voltage. The calculation formula is shown in Equation (11).…”

“…The different parasitic capacitance values of the two winding structures are due to the potential difference between the upper and lower adjacent conductor layers. Assuming that the voltage on the planar inductor is 12 V, the parasitic capacitance values of the traditional and interleaved winding designs are calculated by Equation (11). The parasitic capacitance of the resonant inductor with traditional winding is 257 pF, and the parasitic capacitance of the resonant inductor with interleaved winding is 117 pF.…”

“…[8][9][10] give an accurate calculation model of inductor parasitic capacitance and verify it in a DAB active full-bridge converter. In [11], the causes of planar inductor parasitic capacitance were analyzed; a planar inductor structure optimization scheme was designed; and the parasitic capacitance was reduced. Moreover, Ref.…”

Wide-Range Operation of High Step-Up DC-DC Converters with Multimode Rectifiers

“…However, in practice the multi-tap transformer design suffers from the copper cross-section area increase caused by the connection terminals to the winding taps. Despite having a similar copper cross-section area, a higher number of turns of the multi-tap winding requires more winding layers, which is a significant drawback due to the much-increased parasitic proximity and skin effects, increasing the winding losses considerably [23,24]. The final consideration in favor of the MMR approach is that the VDR mode, where the transformer winding experiences the highest current stress, is used in the range where the input current is limited, and thus the converter operates at the power levels below the rated maximum.…”