What factors should be considered when customizing common-mode chokes?

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2025-09-18

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When designing circuits, if standard off-the-shelf common mode chokes do not meet the requirements, product customization becomes necessary. This ensures the common mode choke can satisfy the circuit's needs for electromagnetic interference (EMI) suppression, structural layout, and other specifications. Customizing a common mode choke requires selecting appropriate materials and a product structure based on the actual application scenario and required performance parameters. For a design engineer, clearly defining these needs is a critical first step.


CODACA common mode chokes


1. Definition of a Common Mode Choke

First, let's clarify what a common mode choke is.

Definition: A common mode choke, also known as a common mode choke coil, consists of two coils with the same number of turns wound in opposite directions on a single closed magnetic core. It presents a very high impedance to common mode noise, allowing it to suppress common mode interference. Conversely, it has a very low impedance to differential mode signals, causing almost no suppression of the desired signal.

Principle : According to the right-hand rule, when a common mode current flows through the windings, the magnetic fields generated by the two coils reinforce each other (Figure 1). This causes the entire component to exhibit high impedance, which attenuates the interference signal. When a differential mode current flows, the two magnetic fields generated are equal and opposite, canceling each other out (Figure 2). This allows the desired current signal to pass through unaffected. For this reason, common mode chokes are used in circuits to suppress common mode interference.


When common mode current flows, the magnetic fields reinforce each other

Figure 1: When common mode current flows, the magnetic fields reinforce each other


When differential mode current flows, the magnetic fields cancel each other out

Figure 2: When differential mode current flows, the magnetic fields cancel each other out


2. Main Categories of Common Mode Chokes

Common mode chokes can be divided into two main categories based on their application: signal line common mode chokes and power line common mode chokes.

Below is the standard product classification and corresponding product models for common mode chokes on the Codaca official website. The page can be accessed here:

https://www.codaca.com/Productsctr_Common-Mode-Choke.html


Data Line Common Mode Choke

Figure 3: Data Line Common Mode Choke


Power Line Common Mode Inductor

Figure 4. Power Line Common Mode Inductor


Parameter Interpretation:

Taking Codaca CPSQ1515L-203 Common Mode Inductor as an example:


Table 1: Characteristic Parameters of the CPSQ1515L-203 Common Mode Choke

What factors should be considered when customizing common-mode chokes?


① Inductance: Under the same frequency and parasitic capacitance conditions, a larger inductance results in higher impedance.

② Impedance: Higher impedance provides better filtering performance. The impedance value varies at different frequencies.


Impedance vs. Frequency Characteristic Curve for the CPSQ1515L-203 Common Mode Choke

Figure 5: Impedance vs. Frequency Characteristic Curve for the CPSQ1515L-203 Common Mode Choke


③ DC Resistance (DCR): The resistance exhibited across the inductor under DC conditions; generally, lower DCR is preferred.

④ Rated Current: The maximum current the inductor can carry continuously without overheating.

⑤ Rated Voltage: The voltage rating at which the circuit is designed to operate normally.

⑥ Hi-pot (Withstand Voltage): The voltage that the winding can withstand between turns or between windings for a specified period without breakdown.

⑦ Operating Temperature Range: The temperature range within which the component can operate reliably.


3. The 6 Steps of Common Mode Choke Customization

When standard products cannot meet a customer's needs, customization of the common mode choke is required. Having clarified the definition, principle, and parameters of common mode chokes, we will now discuss how to customize a suitable one for a client.


Step 1: Clarify Customer Requirements

Application Scenario Analysis: Conduct a comprehensive analysis of the common mode choke’s use case. This includes the specific application (which determines the required product grade—automotive or industrial), operating voltage, current, and operating frequency. These factors will directly influence the design and selection of the common mode choke.


Step 2: Determine Characteristic Parameters

Inductance: Inductance is one of the most important performance parameters of a common mode choke and directly impacts its application. The required inductance must be determined based on the specific use case.

The formula to calculate the minimum required inductance for a common mode choke in a filter circuit (ignoring parasitic capacitance) is:

What factors should be considered when customizing common-mode chokes?


Where What factors should be considered when customizing common-mode chokes? is the required impedance value at frequency What factors should be considered when customizing common-mode chokes?.

Impedance: The ability of a common mode choke to suppress common mode noise is closely related to its impedance. The appropriate impedance value must be determined based on the desired filtering effect.


Step 3: Select Appropriate Materials and Product Structure

Core Material: The core is used to enhance the magnetic permeability of the coil, which increases the magnetic induction intensity within the winding and thus raises the inductance value. Materials with high magnetic permeability, such as high-permeability ferrite, amorphous, or nanocrystalline materials, are typically chosen. The choice of core material directly affects the inductor's performance, and a suitable material can also help reduce the product's physical size.

Coil Material: The coil is usually wound from copper wire. The number of turns and wire diameter are designed based on the required inductance and effective current value.


The formula for calculating inductance is:

What factors should be considered when customizing common-mode chokes?


What factors should be considered when customizing common-mode chokes? - Permeability of free space

What factors should be considered when customizing common-mode chokes? - Relative permeability of the core

What factors should be considered when customizing common-mode chokes? - Effective cross-sectional area of the core

What factors should be considered when customizing common-mode chokes? - Effective magnetic path length of the core

What factors should be considered when customizing common-mode chokes? - Number of coil turns


As shown by the formula, to achieve product miniaturization, one can consider using a core with higher magnetic permeability to reduce the core's volume.

Structural Design: Based on the spatial layout of the customer's circuit board, rationally design a vertical or horizontal product structure and choose a through-hole or surface-mount package type to ensure the choke can be correctly installed.


Step 4: Reference Safety Standards

Refer to safety standards such as IEC 60664-1 or the customer's internal standards.


Step 5: Consider Environmental Factors

The operating environment also affects the electrical performance of the inductor. When customizing a common mode choke, consider environmental factors like temperature, humidity, and the cooling method to ensure it operates stably in its actual application.


Step 6: Performance Testing and Optimization

After customization, the common mode choke must undergo performance testing, including tests for inductance, impedance, and other parameters. If the test results do not meet the requirements, the design must be optimized until it satisfies the application's needs.


4. Conclusion

In summary, customizing a suitable common mode choke requires a comprehensive consideration of multiple factors, including customer application needs, materials and structure, performance parameters, safety requirements, environmental factors, and performance testing and optimization. Only through scientific analysis and rational design can one ensure that the customized common mode choke will meet the demands of the actual application.

The R&D team at Codaca Electronics has extensive experience in the custom development of common mode chokes. We can quickly provide matching product solutions for different customer application scenarios. We welcome you to contact us for consultation and more information.


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