Multilayer Transformer Shield Layout for Common-Mode Noise Cancellation
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Solution Overview
Problem
Current magnetic transformers in power converters occupy a significant volume and contribute to the large size of AC-DC adapters, while also generating common-mode noise due to parasitic capacitance between primary and secondary windings, which complicates noise reduction and increases costs.
Innovation Solution
The integration of a magnetic core with primary and secondary multilayer boards, where the primary board embeds primary windings and auxiliary windings, and the secondary board embeds secondary windings, with a controlled dual function shield connected to the primary quiet termination to minimize parasitic capacitance and common-mode noise, allowing for the cancellation of noise between primary and secondary grounds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If traditional magnetic transformers are used in power converters, then power transfer function is achieved, but the device occupies significant volume (20-40% of adapter size)
Solution Approach 1:
The patent transitions from traditional three-dimensional wire-wound transformer geometry to a planar two-dimensional structure where windings are formed on flat PCB substrates. The magnetic core is also planar with windings arranged in layers on the same plane, fundamentally changing the spatial dimensionality and enabling compact integration while maintaining power transfer function
Solution Approach 2:
The patent combines multiple previously separate components into a single integrated planar transformer structure. The primary and secondary windings, auxiliary windings, and magnetic core are merged into one compact planar assembly, eliminating the need for separate magnetic elements and reducing overall volume
2Object-affected harmful factors
If traditional transformer winding structures are used, then power transfer is achieved, but parasitic capacitance between primary and secondary windings generates common-mode noise
Solution Approach 1:
The patent introduces a magnetic shielding layer as an intermediary structure positioned between the primary and secondary windings. This shielding layer acts as a mediator that blocks electromagnetic coupling and reduces parasitic capacitance effects, thereby suppressing common-mode noise while allowing power transfer to continue through the magnetic core
Solution Approach 2:
The patent extracts and separates the magnetic shielding function from the traditional winding structure by implementing it as a distinct planar layer. This extracted shielding layer can be independently optimized and positioned to specifically address common-mode noise without interfering with the power transfer windings
3Device complexity
If multiple separate magnetic elements are used in flyback topology, then energy storage and transfer functions are achieved, but device complexity and component count increase
Solution Approach 1:
The patent combines the energy storage function and power transfer function into a single planar transformer structure. The primary windings store energy during the on-time while the secondary windings transfer energy during off-time, eliminating the need for separate magnetic elements and reducing component count while maintaining reliable energy storage and transfer
Solution Approach 2:
The planar transformer structure serves multiple functions simultaneously: it acts as both the energy storage element and the power transfer element, and also provides magnetic shielding for noise reduction. This multi-functionality reduces overall device complexity while maintaining all necessary functions
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 the size of magnetic components, decreases common-mode noise, and lowers the number of layers in the multilayer PCB, thereby reducing costs and improving efficiency in power converters.
Implementation Method 1
the flyback transformer provide two functions. The first function is to transfer power from primary to secondary during the off time of the main switch while storing energy in the transformer during the on time of the main switch
Implementation Method 2
a controlled dual function shield connected to the primary quiet termination to minimize parasitic capacitance and common-mode noise
Data Source
AI summary
A magnetic structure in a power converter includes at least two multilayer boards, such as a primary board containing the primary windings and some auxiliary windings, and a secondary board containing the secondary windings and some auxiliary windings. The primary and secondary boards are on top of each other. On the layer on the primary board adjacent to the secondary board, is a dual function shield to reduce the total common mode noise in the converter towards zero. The controlled dual function shield can be placed on the secondary board on the layer adjacent to the primary board, and in some embodiments can be placed on both primary and secondary board on the layers adjacent to the other board. The embodiments herein offer a very good solution for cost reduction of the planar transformers and offers an avenue for total elimination of the common mode noise in a power converter.