Planar Multilayer Transformer Shielding for Low Common-Mode Noise
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Solution Overview
Problem
Existing power adapters for electronic devices, such as laptops and tablets, are large due to the significant volume occupied by magnetic transformers and input EMI filters, hindering miniaturization efforts while maintaining efficiency and cooling.
Innovation Solution
A system for reducing common-mode noise in power supplies includes a switch mode power supply with a planar multilayer transformer, primary and secondary windings, and shields with fractional and multiple turns to minimize displacement current and eliminate the need for common mode chokes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If traditional magnetic transformers are used in power adapters, then power transformation function is achieved, but adapter volume increases significantly
Solution Approach 1:
The patent transitions from traditional three-dimensional magnetic core transformers to planar transformers utilizing PCB layers. The transformer windings are distributed across multiple PCB layers (primary windings on odd layers, secondary windings on even layers), transforming the magnetic coupling from volumetric to planar geometry. This dimensional change enables significant volume reduction while maintaining power transformation capability through controlled impedance and parasitic capacitance management.
2Volume of stationary object
If transformer size is reduced for miniaturization, then adapter volume decreases, but electromagnetic noise increases
Solution Approach 1:
The patent introduces intermediate shielding layers and ground references between primary and secondary windings on adjacent PCB layers. These intermediate structures act as mediators that control electromagnetic coupling and suppress noise. The controlled parasitic capacitance between layers, combined with proper grounding strategies, filters high-frequency noise while maintaining the compact planar structure.
Solution Approach 2:
The patent implements differential winding arrangements where adjacent turns on the same layer are wound in opposite directions. This creates local magnetic field cancellation effects that reduce electromagnetic radiation and noise. The local quality of each winding section is optimized to minimize EMI while contributing to the overall power transformation function.
3Volume of stationary object
If planar transformer structure is used to reduce volume, then adapter size decreases, but EMI filter components are still required occupying additional space
Solution Approach 1:
The patent merges the EMI filtering function directly into the transformer structure by integrating shield layers and ground references as part of the transformer assembly itself. The shielding layers between primary and secondary windings serve dual purposes: magnetic coupling and EMI filtering. This integration eliminates the need for separate external EMI filter components, reducing overall device complexity and volume.
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 approach reduces common-mode noise and allows for a smaller, more efficient power converter design, achieving higher power density and compliance with electromagnetic interference (EMI) standards.
Implementation Method 1
a transformer core having at least two magnetic legs, a planar multilayer transformer having primary windings and primary auxiliary windings which report to the primary and surrounds the magnetic legs and secondary windings and secondary auxiliary windings which report to the secondary and surrounds the magnetic legs
Implementation Method 2
a first shield, using fractional turns, placed on a first shield layer having a center tap which is connected to the primary ground, and two terminations on left and right sides of the center tap... and a second shield on a second shield layer, wherein the second shield contains a plurality of turns
Data Source
AI summary
A planar multilayer transformer in a power converter wherein winding arrangements and placement of shields reduces common mode noise to a level wherein the common mode inductor in an input EMI filter can be reduced and even eliminated decreasing the power dissipation and increasing the power density. The methods presented herein can reduce the number of layers in the multilayer PCB by eliminating the layers used for the shields and still be in full compliance with EMI requirements.