Transformer Auxiliary Float Winding for Common Mode Noise Reduction

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Solution Overview

Problem

Existing power supply transformers struggle to effectively reduce common mode (CM) noise, particularly in sensitive applications like touch screen devices, where conventional methods fail to adequately cancel or redirect CM noise, leading to interference and performance issues.

Innovation Solution

A modified transformer structure incorporating an auxiliary float winding with externally extended float wires on an isolation sheet, which forms a path to compensate, block, or redirect CM noise by utilizing distributed capacitance, thereby reducing the impact of CM noise on the output load.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Object-affected harmful factors

If conventional transformer structures are used, then the device complexity is low, but the common mode noise reduction capability is insufficient

Engineering Contradiction:

Improvecommon mode noiseVSAvoidtransformer structure

Core Design Contradiction:

Object-affected harmful factorsVSDevice complexity

Solution Approach 1:

The transformer structure is segmented by adding an auxiliary winding with a specific tap point, dividing the winding into multiple sections. This segmentation allows different portions of the winding to serve different functions in CM noise cancellation, enabling the transformer to simultaneously perform power transfer and noise reduction without requiring a completely separate CM choke device.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The auxiliary winding with tap connection serves multiple functions: it provides the primary power transfer function while simultaneously creating counter-phase voltages for CM noise cancellation. This multi-functionality eliminates the need for separate dedicated CM noise reduction components, reducing overall device complexity while improving noise performance.

Inventive Principle:

Principle #6Universality (Multi-functionality)

2Object-affected harmful factors

If additional windings are added to the transformer, then the common mode noise reduction capability is improved, but the manufacturing complexity increases

Engineering Contradiction:

Improvecommon mode noiseVSAvoidtransformer assembly

Core Design Contradiction:

Object-affected harmful factorsVSEase of manufacture

Solution Approach 1:

The CM noise cancellation function is merged with the existing transformer structure by adding an auxiliary winding that shares the same magnetic core and physical space. The tap connection on the auxiliary winding allows it to be integrated into the existing winding assembly process, eliminating the need for separate mounting and connection steps that would increase manufacturing complexity.

Inventive Principle:

Principle #5Merging (Combining)

3Loss of information

If the transformer structure is modified with external float wires, then the signal-to-noise ratio is improved, but the device complexity increases

Engineering Contradiction:

Improvesignal-to-noise ratioVSAvoidtransformer structure

Core Design Contradiction:

Loss of informationVSDevice complexity

Solution Approach 1:

The tap connection on the auxiliary winding acts as an intermediary that extracts a portion of the winding voltage to create the counter-phase signal needed for CM noise cancellation. This intermediary approach allows the system to generate the necessary canceling signal without requiring complex external circuitry, maintaining a relatively simple device structure while improving signal-to-noise ratio.

Inventive Principle:

Principle #24Intermediary (Mediator)

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

The proposed transformer design significantly reduces CM noise, as demonstrated by test results showing a decrease in CM noise spectrum below regulatory thresholds, improving the signal-to-noise ratio and enhancing the performance of devices like touch screen chargers.

Implementation Method 1

which forms a path to compensate, block, or redirect CM noise by utilizing distributed capacitance

Methodology Applied

Scientific EffectDistributed capacitance: Capacitance

Implementation Method 2

During operation the transformer allows the transfer of energy between an input side (referred to as a primary side) of the power supply and an output side (referred to as the secondary side) of the power supply

Methodology Applied

Scientific EffectElectromagnetic induction: Electromagnetic Induction

Data Source

PatentUS11164696B2Low common mode noise transformer structure with external float wire mount

Publication Date: 2021.11.02 POWER INTEGRATIONS INC

AI summary

A transformer structure is disclosed to reduce common mode noise on an output load. The transformer structure includes a bobbin mounted on a magnetic core, a plurality of windings wound around the bobbin. The plurality of windings include a primary winding coupled to receive an input voltage, a secondary winding coupled to an output load; and a floating auxiliary winding located between the primary and secondary winding. The floating auxiliary winding includes a first terminal and a second terminal coupled to a pair of external float wires extended towards an isolation mounting sheet placed adjacent to an exterior top surface of the transformer structure. The pair of external float wires forms parallel adjacent and open-ended conductive traces with a predefined pattern on the isolation mounting sheet placed above the exterior surface of the transformer structure.