Transformer Shield Neutralization Signal Common Mode Noise
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Solution Overview
Problem
Switched-mode power supplies experience significant common mode noise due to voltage differences between transformer windings, which can interfere with devices and are challenging to mitigate, especially in compact and cost-sensitive applications like smartphone chargers, where conventional filters may not be feasible.
Innovation Solution
Incorporating a conductive shield between the primary and secondary windings of the transformer and a neutralization signal generator circuit that applies an adjustable amplitude and phase neutralization signal to the shield to reduce common mode noise.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If conventional EMI filters are used to reduce common mode noise, then noise attenuation is improved, but device size and cost increase
Solution Approach 1:
A conductive shield is introduced as an intermediary component between the primary and secondary windings of the transformer. The shield acts as a mediator that blocks and bypasses inter-winding coupling components, preventing common mode noise from coupling through the transformer while maintaining a compact form factor suitable for smartphone chargers.
Solution Approach 2:
The harmful common mode noise coupling path is extracted and isolated by placing a conductive shield between the primary and secondary windings. The shield captures and redirects the noise current through dedicated paths (Y-capacitors to ground) separate from the signal paths, effectively removing the noise from the output without requiring large external filters.
2Object-affected harmful factors
If transformer winding shields are used to block inter-winding coupling, then common mode noise is reduced, but device complexity and cost increase
Solution Approach 1:
The conductive shield serves multiple functions simultaneously: it acts as an EMI barrier between windings, provides a controlled impedance path for noise current, and works in conjunction with Y-capacitors to create an effective noise filtration system. This multi-functionality reduces the need for additional separate components, thereby managing complexity while achieving effective noise reduction.
Solution Approach 2:
The conductive shield is nested within the transformer structure itself, positioned between the primary and secondary windings. This integration of the shielding function within the existing transformer geometry avoids adding external bulk or complex external shielding structures, maintaining a compact and simple overall device design.
3Object-affected harmful factors
If Y-capacitors are used for local bypass of interference current, then externally measureable interference is reduced, but common mode noise coupling through transformer remains
Solution Approach 1:
The conductive shield is positioned in advance between the primary and secondary windings to intercept and redirect noise current before it can couple through the transformer. By placing the shield upstream in the noise path, the majority of inter-winding coupling is prevented at the source, reducing the burden on downstream Y-capacitors and further lowering externally measureable interference.
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
Effectively cancels common mode noise between windings, improving the performance of power supplies by minimizing interference and ensuring reliable operation in noise-sensitive applications, even in smaller form factors.
Implementation Method 1
Transformer winding shields may be used to block and bypass inter-winding coupling components completely, partially, etc.
Implementation Method 2
EMI noise cancellation may also be used
Data Source
AI summary
An example switched-mode power supply includes an input for receiving an input voltage from a voltage source, an output for providing an output voltage to a load, and a transformer having a primary winding, a secondary winding, and a conductive shield disposed between the primary winding and the secondary winding. The power supply also includes a neutralization signal generator circuit coupled to the conductive shield to apply a neutralization signal to the conductive shield to reduce a common mode noise between the primary winding and the secondary winding of the transformer. The neutralization signal has an adjustable amplitude and/or phase. Other example power supplies and methods are also disclosed.