The number of turns in a common mode choke (CMC) is a critical parameter that affects its performance, particularly in terms of impedance and noise suppression capabilities. The turns determine the inductance of the choke, which in turn influences its ability to block common mode noise while allowing differential mode signals to pass through with minimal attenuation.

From the provided search results, we can gather some insights into the number of turns used in different configurations of common mode chokes:

1. Single-Layer Winding: In one study, a common mode choke was wound with 22 turns of round copper wire with a diameter of 0.8mm. This configuration showed the lowest leakage inductance with a higher self-resonant frequency (SRF).

2. Different Location Winding: Another experiment compared winding on the longer side versus the shorter side of a rectangular core body. With the same round wire of 0.4mm diameter and 48 turns, the short side winding resulted in higher leakage inductance and was more difficult to wind compared to long-side winding.

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4. Thicker Cables: For thicker cables, such as RG-213/U coax and 3 × AWG 14, 60-Hz power cords, a string of 22 beads has an impedance greater than 1 kΩ from 1.8 MHz through at least 20 MHz and probably well beyond 30 MHz. This suggests that the number of turns can be adjusted based on the cable's thickness and the desired frequency range for impedance.

5. Bifilar-Wound Toroids: In a balun circuit, each of the six ferrite toroidal-core chokes was wound with seven turns of the bifilar transmission line. Each ferrite toroid was a Fair-Rite Products p/n 5961003801 (mix 61).

These examples illustrate that the number of turns in a common mode choke can vary significantly depending on the design goals and the specific application. The turns are chosen to achieve the desired impedance at the frequencies of interest, which is crucial for effective noise suppression. It's important to note that the number of turns is just one of several factors that influence the performance of a common mode choke, with others including the type of core material, the wire size, and the physical configuration of the windings.

How many turns for common mode choke？

Common Mode Chokes (CMCs) are electromagnetic interference (EMI) suppression components used in electronic circuits to block high-frequency noise common to two or more data or power lines while allowing the desired DC or low-frequency signals to pass through.

common mode chokes operate on the principle of magnetic coupling. They consist of two or more windings wrapped around a magnetic core. When a differential signal is applied, the magnetic fields generated by the windings oppose each other, resulting in minimal impedance. However, when common mode choke noise is present, the magnetic fields reinforce each other, creating high impedance that effectively blocks the unwanted noise.

In normal or differential mode, current travels in one direction on one line and in the opposite direction on the return line. In common mode, noise current travels in the same direction on both lines. The combined magnetic flux in the core creates an opposing field that blocks the noise. This means that common mode chokes allow differential mode signals to pass with minimal attenuation while attenuating common mode noise.

common mode chokes are crucial for improving electromagnetic compatibility (EMC) in electronic systems. They suppress unwanted noise while permitting desired signals to pass, contributing significantly to the reliability and performance of various applications. The effectiveness of common mode chokes in filtering out common mode noise makes them vital components in applications such as power supplies, data communication lines, and other electronic systems where EMI can cause interference and performance issues.