Common Mode Choke Winding Overlap for Lower Parasitic Capacitance
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Solution Overview
Problem
Common mode chokes with windings wound in multiple layers face increased parasitic capacitance between layers, leading to altered impedance and resonance frequency, necessitating larger cores and higher costs, while maintaining effective common mode noise reduction across a broad frequency range.
Innovation Solution
The windings are arranged such that the difference between the highest and lowest turn numbers in the second layer and the section of the first layer it is wound on is less than or equal to 50% of the first layer's turns, minimizing parasitic capacitance and allowing for a smaller, more elegant design without compromising noise reduction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the number of turns in the windings is increased to achieve high inductance for good common mode noise reduction, then the common mode noise suppression is improved, but the parasitic capacitance between turns increases leading to lower resonance frequency and degraded high frequency performance
Solution Approach 1:
The winding is divided into two separate layers (first layer and second layer) with the second layer wound around a section of the first layer. This segmentation allows control of parasitic capacitance by limiting the overlap between layers to a specific section rather than the entire winding length, thus managing the resonance frequency while maintaining high inductance through sufficient total turns.
2Manufacturing precision
If the windings are arranged in multiple layers to fit more turns on the core, then the inductance is increased, but the parasitic capacitance between layers significantly alters the impedance and resonance frequency
Solution Approach 1:
The second layer is wound around only a section of the first layer rather than the entire first layer. This local arrangement concentrates the parasitic capacitance effect to a specific region, allowing the rest of the winding to maintain stable impedance characteristics. The local sectioned overlap provides controlled parasitic capacitance while preserving overall impedance stability across the frequency range.
3Manufacturing precision
If a larger magnetic core is used to accommodate more turns without multiple layers, then the inductance is maintained with lower parasitic capacitance, but the device size and cost increase
Solution Approach 1:
The second layer is wound around a section of the first layer, creating a nested structure where one layer is partially enclosed by another. This nesting allows efficient use of the magnetic core space, accommodating the required number of turns in a compact configuration without requiring a larger core, thus maintaining small device size while achieving the necessary inductance.
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 arrangement minimizes the effect of parasitic capacitance between layers, maintaining high impedance at lower frequencies and reducing noise effectively across the frequency range, while allowing for a smaller and less expensive enclosure.
Implementation Method 1
common mode currents will flow in the same winding direction. The two windings have the same number of turns, and each winding is arranged in series with one of the supply lines. By common mode noise, currents flow in the same direction through each of the two windings, thus creating equal and in-phase magnetic fields, which add together.
Implementation Method 2
by differential mode signals, including the desired signal such as the supply current delivered to the converter, the two currents will be equal and flow in opposite directions, and the magnetic flux produced in the core by these currents will subtract and tend to cancel each other out since the windings are negative coupled.
Implementation Method 3
a common mode choke has a more complex behaviour because of parasitic capacitance or stray capacitance between the individual turns of the windings due to their proximity to each other, and the inductor will act as though it includes a parallel capacitor. The parasitic capacitance changes the impedance of the choke by causing parallel resonance between the inductance and the capacitance at a resonance frequency.
Data Source
Figure 1~3b
Figure 4a~5c
Figure 6a~6e
AI summary
A common mode choke (64) comprises a magnetic core (58) and a first (Wab) and a second (Wcd) winding of insulated wire having the same number of turns wound on the magnetic core. The turns of each winding are numbered consecutively and arranged in at least two layers, of which a first layer of turns is wound directly on the magnetic core and a second layer of turns is wound around a section of the first layer. The two layers are arranged such that the difference between the highest number of a turn in the second layer and the lowest number of a turn in the section of the first layer on which the second layer is wound is less than or equal to 50 % of the number of turns in the first layer. In this way, the effect of the parasitic capacitance between the layers is minimized.