PCB Layout for Switching Power Supply EMI Cancellation
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Solution Overview
Problem
Conventional switching power supplies experience significant EMI radiation noise due to LC resonance in the input loop, which existing methods like reducing parasitic capacitance or splitting switches to cancel magnetic fields are unable to completely eliminate, and spectrum spreading has limited effectiveness.
Innovation Solution
A printed circuit board layout featuring a 3D wiring pattern with open ring current paths in opposing directions between layers, connected by conductive members, effectively cancels magnetic fields by overlapping current paths and using a single bypass capacitor, reducing EMI radiation noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-generated harmful factors
If the distance between the bypass capacitor and the semiconductor device is reduced, then the parasitic capacitance component and magnetic field are reduced, but it is not possible to completely eliminate the magnetic field
Solution Approach 1:
The patent transitions from a planar layout to a three-dimensional stacked layout, placing the bypass capacitor in a different layer (second layer) than the semiconductor device (first layer). This vertical arrangement creates overlapping current paths that generate opposing magnetic fields, achieving complete cancellation rather than just reduction. The conductive members connect the capacitor terminals to corresponding device terminals across layers, forming closed loop current paths that overlap in the vertical dimension.
2Object-generated harmful factors
If two bypass capacitors are used to cancel magnetic fields through symmetric input loops, then magnetic field cancellation is achieved, but cost increases unnecessarily
Solution Approach 1:
The patent merges the functions of two separate bypass capacitors into a single bypass capacitor. By placing one capacitor in the second layer and connecting it to both high-side and low-side switches through conductive members, the single capacitor serves dual purposes: filtering noise for both switching nodes and generating the opposing magnetic field for cancellation. This consolidation reduces component count and cost while maintaining effective magnetic field cancellation.
3Object-generated harmful factors
If spectrum spreading is applied to the driving frequency, then EMI radiation noise is suppressed to some extent, but the effect is limited and not thorough
Solution Approach 1:
The patent converts the harmful magnetic fields generated by switching currents into a beneficial cancellation mechanism. By deliberately designing the current paths to overlap in opposite directions, the magnetic fields that would normally radiate as EMI noise are instead made to neutralize each other. This transforms the problematic electromagnetic fields into a solution that actively suppresses EMI radiation noise, achieving thorough suppression beyond the limited effect of spectrum spreading.
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 significantly suppresses EMI radiation noise, avoiding the cost increase of multiple capacitors and achieving a more thorough cancellation of magnetic fields, making it suitable for stringent noise standards like CISPR25.
Implementation Method 1
the direction of the current that flows across the first current path and the direction of the current that flows across the second current path are opposite to each other
Implementation Method 2
this configuration significantly suppresses EMI radiation noise, avoiding the cost increase of multiple capacitors and achieving a more thorough cancellation of magnetic fields
Data Source
AI summary
A printed circuit board has: a first wiring pattern laid in a first layer such that, when a predetermined component is mounted in a predetermined mounting region, a first current path in an open ring shape leading from a first end to a second end is formed; a second wiring pattern laid in a second layer different from the first layer such that a second current path in an open ring shape leading from a third end to a fourth end is formed; a first conductive member formed between the second and third ends; and a second conductive member formed between the first and fourth ends. The first and second wiring patterns are so laid that, as seen in their respective plan views, the directions of the currents flowing across the first and second current paths, respectively, are opposite to each other.