PCB Planar Transformer Shielding Layer Width for EMI Consistency

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Solution Overview

Problem

PCB planar transformers in switching mode power supplies face challenges with parasitic capacitance between primary and secondary windings, leading to significant EMI performance issues due to manufacturing tolerances, which affect the consistency of EMI performance in mass-produced switch power supplies.

Innovation Solution

A PCB planar transformer design with a shielding layer between the primary and secondary winding layers, where the conductor width in the shielding layer is wider than the winding trace widths, reducing the impact of processing tolerances on distributed capacitance and maintaining designed overlapping areas, thereby controlling variance in EMI performance.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Volume of moving object

If a PCB winding transformer is used with compact structure, then high power density and low profile form factor are achieved, but parasitic capacitance between primary and secondary windings increases, seriously impacting EMI performance

Engineering Contradiction:

Improvepower densityVSAvoidEMI performance

Core Design Contradiction:

Volume of moving objectVSObject-affected harmful factors

Solution Approach 1:

A shielding layer is introduced as an intermediary element between the primary and secondary windings. This shielding layer, positioned in the insulation layer between the two windings, acts as a mediator to reduce the parasitic capacitance coupling between them, thereby improving EMI performance while maintaining the compact PCB transformer structure

Inventive Principle:

Principle #24Intermediary (Mediator)

Solution Approach 2:

The shielding layer is strategically positioned only in specific regions where parasitic capacitance is most problematic. By placing the shielding layer locally between the primary and secondary windings in high-stress areas, the solution targets the specific problem regions without requiring complete structural redesign of the entire transformer

Inventive Principle:

Principle #3Local quality

2Ease of manufacture

If manufacturing tolerances are considered in PCB fabrication, then production flexibility is maintained, but the overlapping area between windings and shielding layers varies, causing variance in distributed capacitance and EMI performance

Engineering Contradiction:

Improveproduction flexibilityVSAvoidoverlapping area consistency

Core Design Contradiction:

Ease of manufactureVSManufacturing precision

Solution Approach 1:

The shielding layer is designed and positioned in advance during the PCB layer design stage, with predetermined locations and dimensions. This preliminary positioning ensures that even when manufacturing tolerances cause variations in the actual overlapping areas between windings and shielding layers, the EMI performance variance is minimized because the shielding structure is already optimally configured

Inventive Principle:

Principle #10Preliminary action

Solution Approach 2:

The shielding layer serves as a pre-configured protective structure that compensates for potential manufacturing variations. By having the shielding layer in place before final assembly and operation, it cushions against the adverse effects of tolerance variations, ensuring consistent EMI performance across mass-produced units

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

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 design significantly reduces the influence of manufacturing tolerances on distributed capacitance between the primary and secondary sides, enhancing the consistency of EMI performance across switching power supplies.

Implementation Method 1

at least one shielding layer, each located between the primary winding layer and the adjacent secondary winding layer, wherein the shielding layer is formed with a conductor therein

Methodology Applied

Scientific EffectElectrostatic shielding: Faraday Cage

Data Source

PatentUS10128760B2PCB planar transformer and converter using the same

Publication Date: 2018.11.13 DELTA ELECTRONICS INC(CN)

AI summary

A PCB planar transformer, comprising: at least one primary winding layer, each formed with a primary winding therein, wherein wire traces constituting the primary winding have a first horizontal width; at least one secondary winding layer, each formed with a secondary winding therein, wherein wire traces constituting the secondary winding have a second horizontal width; and at least one shielding layer, each located between the primary winding layer and the adjacent secondary winding layer, wherein the shielding layer is formed with a conductor therein, and the conductor in the shielding layer has a third horizontal width, wherein at least one of the first horizontal and the second horizontal width is smaller than the third horizontal width of the conductor in the shielding layer.