Multilayer Transformer PCB Structure Reducing Eddy Current Losses
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Solution Overview
Problem
Multilayer transformers in power converters face significant skin and eddy current effects due to the concentration of current near the outer perimeter of conductor windings, leading to inefficiencies and increased losses, particularly at high frequencies.
Innovation Solution
The multilayer transformer structure is enhanced by vertically aligning the secondary current pathways with the primary current pathways within the PCB stack, with rectifying transistors positioned to overlap the primary winding conductors, reducing proximity effects and eddy current losses by maximizing the proximity of the secondary and primary currents.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If current flows through outer perimeter of conductor windings, then current concentration occurs, but skin effect and eddy current losses increase
Solution Approach 1:
The patent applies vertical stacking of conductor windings in the Z-dimension to distribute current pathways throughout the conductor cross-section. By creating multiple vertically stacked layers with interleaved primary and secondary windings, the current is forced to utilize pathways distributed across different vertical positions, effectively utilizing the third dimension to reduce current concentration at the outer perimeter and minimize skin and proximity effects.
Solution Approach 2:
The patent segments the continuous winding into multiple discrete vertical layers stacked along the Z-axis. Each layer contains conductors at different vertical positions, and the interleaved arrangement creates segmented current pathways that distribute current density more uniformly across the conductor cross-section, reducing the harmful concentration effect at outer perimeters.
2Ease of manufacture
If rectifying transistors are positioned outside transformer footprint, then ease of assembly is improved, but proximity effects increase
Solution Approach 1:
The patent merges the rectifying transistors with the transformer structure by positioning them vertically above the secondary winding conductors within the transformer footprint. This integration causes the transistor drain regions to overlap with the secondary conductors in the vertical dimension, creating direct vertical current pathways that minimize horizontal current flow and reduce proximity effects while maintaining compact assembly.
Solution Approach 2:
The patent utilizes the vertical Z-dimension to position rectifying transistors above the secondary windings rather than placing them horizontally outside the transformer footprint. This vertical positioning creates overlapping regions where transistor drain areas intersect with secondary conductor areas in the vertical stack, establishing direct vertical current pathways that reduce proximity effects.
3Power
If operating frequency is increased, then power density is improved, but skin effect and eddy current losses increase
Solution Approach 1:
The patent employs vertical stacking of multiple conductor layers in the Z-dimension to create distributed current pathways throughout the transformer volume. This three-dimensional current distribution allows high-frequency operation by providing multiple parallel pathways that reduce current concentration and minimize skin and proximity effects, enabling higher power density at elevated frequencies.
Solution Approach 2:
The patent segments the winding structure into multiple vertical layers with interleaved primary and secondary conductors. This segmentation creates distributed current pathways that reduce current density concentration, allowing the transformer to operate efficiently at high frequencies with reduced skin and eddy current losses, thereby achieving higher power density.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This configuration reduces AC resistance by approximately 50% and improves efficiency by minimizing proximity effects, as shown in the graphs of AC resistance versus frequency and efficiency versus power, leading to enhanced power conversion performance.
Implementation Method 1
A transformer structure can be integrated as part of a multilayer printed circuit board by having each 'coil' in the transformer represented as a coil shaped conductor patterned on a different layer of the PCB
Implementation Method 2
When operating at high frequencies, for example greater than or equal to 200 KHz, there are significant skin effects and eddy current effects associated with the conductor windings in the multilayer transformer. Skin effect in this case is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current density is largest near the outer perimeter edge of the conductor
Implementation Method 3
When operating at high frequencies, for example greater than or equal to 200 KHz, there are significant skin effects and eddy current effects associated with the conductor windings in the multilayer transformer
Implementation Method 4
The larger the current, the greater the number of rectifying transistors is needed. The number of rectifying transistors are also dependent on multiple other factors including the output voltage, the MOSFET design and package, and a target application load profile
Data Source
AI summary
A power conversion circuit has a multilayer transformer and a plurality of rectifying transistors coupled to the secondary windings of the multilayer transformer. The multilayer transformer is formed as multiple layers within a PCB stack, where primary winding conductors and secondary winding conductors are vertically aligned and stacked. The secondary winding conductors are constructed to have one or more secondary winding arms that provide area to which the plurality of rectifying transistors are physically connected. The primary winding conductors are constructed to have a primary winding arm. A footprint of each primary winding conductor is configured to substantially overlap an entire footprint of each of the secondary winding conductors. As such, an entirety of the secondary current flowing through the secondary winding conductors is vertically aligned with the primary winding conductors, and therefore with the primary current flowing through the secondary winding conductors.