![]() However, the high frequency electronic noise currents which are of much lower amplitude and riding on the main positive and return line will encounter high impedance from the COMMON MODE CHOKE and will be severely attenuated, and therefore filters out. The current rating of COMMON MODE CHOKE is determined by the resistance of the windings which causes temperature rise. For example, a magnetic core that usually saturates at 5 Amps in a differential mode application will not saturate even at 100 Amps in a common mode application provided the 2 currents flowing in and out of the COMMON MODE CHOKE is of equal value or from the same source. Therefore, COMMON MODE CHOKE’s core will not saturate due to the amplitude of the main currents. Since the net magnetic fluxes due to the main current flows are zero, the cores will not go into magnetic saturation in a COMMON MODE CHOKE design. But in real life, there is stray magnetic flux which will minimally attenuate the main currents. ![]() These 2 magnetic fluxes cancel out each other creating a theoretical net flux of zero. But, the direction of the magnetic flux lines created by the current flowing into the first winding is opposite to the flux lines created by the return current into the second windings. The live and return currents are of same magnitude since they are from the same power source. For example, the current from positive terminal of the power source will flow into the COMMON MODE CHOKE’s first winding and the return current will flow into the COMMON MODE CHOKE’s second winding before it gets to the negative terminal of the power source. Please note that CWS is not affiliated with any of these companies.ĬOMMON MODE CHOKE is wound with 2 identical windings, where the current in each winding flows in the opposite direction to each other. Common trade names for Amorphous and Nanocrystalline are METGLASS, FINEMET, HITPERM, VITROPERM, NANOPERM, etc. In high end applications, Co-based amorphous, Fe-based amorphous and Fe-based Nanocrystalline cores materials are used. The most common material used is high permeability manganese zinc ferrites for low cost applications. Typically, COMMON MODE CHOKE is wound on toroidal core, gapless H core or EE core. Figure 1 shows a typical COMMON MODE CHOKE connection. The engineering community has established limits to these electronics noise with standards such as EN 55011.ĬOMMON MODE CHOKE is typically used with capacitors and differential mode inductors to form a complete filter in an electronics circuits. In other words, the common mode choke is used to filter out the electronic noises that are coupled to both the power and the return lines. The common mode choke, as the name suggests, is used to filter out electronic noise that are common to both the power ("live") and the return line. These high frequency noises from SMPS can affect the performance of other electronic devices connected to the same power source, causing potential failures. With the advances in materials and thousands of different common mode products to select for a given application, it is advantages for end users to understand how to select proper devices that are suitable and cost effective that can get the job done.Īlmost all electronics circuits require the use of COMMON MODE CHOKES to filter out the conducted switching and Radio Frequency noise coming from the power sources such as Switching Mode Power Supplies (SMPS) or other line power outlets. It is intentionally written with almost no mathematical expressions, and explained in its most basic and simplest format so that it can be easily understood. This application notes is written for junior engineers, technicians, purchasing managers, program managers who are involved with the design and procurements of Common Mode Chokes and filters.
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