Planar Transformer With Interleaved Windings For High-Frequency DC/DC Converters
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Solution Overview
Problem
High-power and high-frequency DC/DC resonant converters face challenges such as heat dissipation, losses due to skin-depth and proximity effects, and voltage spikes caused by leakage inductance, which hinder achieving high power density and efficiency in transformer designs.
Innovation Solution
The transformer design features interleaved primary and secondary windings with a substrate and conductive layers, solid-filled vias for heat dissipation, and a center-tapped secondary winding configuration to minimize leakage inductance, reducing termination losses and AC losses without the need for a heat sink.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If high switching frequency is used to reduce the size of magnetic components, then power density is improved, but AC loss and DC resistance loss increase due to skin depth effect and proximity effect
Solution Approach 1:
The windings are divided into multiple segments or layers with interleaved structure. This segmentation reduces the effective path length for eddy currents and distributes the current more uniformly, thereby reducing skin depth and proximity effect losses while maintaining high frequency operation for compact size.
Solution Approach 2:
The winding structure is optimized locally by controlling the spacing and arrangement of conductive layers. The interleaved configuration creates local regions with reduced magnetic coupling between adjacent windings, minimizing proximity effect losses in critical areas while maintaining overall compact dimensions.
2Loss of energy
If the distance between secondary windings and synchronous rectifiers is reduced to reduce parasitic impedance, then termination loss is reduced, but manufacturing complexity and reliability risks increase
Solution Approach 1:
The transformer structure is merged with the rectifier circuit board by integrating the secondary winding connections directly onto the PCB substrate. This combination eliminates separate connection elements and reduces the number of discrete components, thereby minimizing parasitic impedance while maintaining reliable electrical connections through standardized PCB mounting techniques.
3Power
If multiple secondary-circuit units are stacked to achieve high power rating, then output power is improved, but total size of transformer assembly increases considerably
Solution Approach 1:
Instead of stacking multiple units vertically in the traditional z-direction, the design utilizes planar integration within the PCB layers and horizontal arrangement of windings. This dimensional reorganization allows multiple secondary circuits to be accommodated in the same footprint area by using available space in the x-y plane and distributing windings across multiple PCB layers, thereby achieving high power output without proportionally increasing the overall assembly volume.
4Productivity
If cylindrical conductive posts are used to connect multiple secondary windings, then power density is improved, but termination losses increase due to non-uniform distances between windings and rectifiers
Solution Approach 1:
The design employs an asymmetric winding arrangement where the secondary windings are positioned at non-uniform intervals and orientations relative to each other, optimized for minimal parasitic inductance to the rectifier connections. This asymmetric configuration allows tailored optimization of each winding's electrical path, reducing termination losses while maintaining compact power density through strategic placement rather than uniform cylindrical stacking.
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 design achieves efficient heat dissipation, reduces losses, and minimizes voltage spikes, resulting in a compact and high-efficiency transformer assembly with improved power density and reduced parasitic impedance.
Implementation Method 1
solid-filled vias for heat dissipation
Implementation Method 2
interleaved primary and secondary windings with a substrate and conductive layers
Implementation Method 3
conductive layers, solid-filled vias for heat dissipation
Data Source
AI summary
A transformer assembly includes a transformer with primary windings located on multiple layers and with secondary windings interleaved with the multiple layers and includes a substrate connected to the transformer and with a first transistor with first, second, and third terminals, in which the first terminal is connected to the secondary windings, the second terminal is connected to an output terminal of the transformer assembly, and the third terminal is a control terminal; first conductive layers; second conductive layers interleaved with the first conductive layers; a first via that is solid filled and that connects the first conductive layers and the first terminal; and a second via that is solid filled and that connects the second conductive layers and the second terminal.