Power supply and DC-to-DC converter designers are faced with more and more electrical noise intrusion issues from nearby higher power systems. This and increasingly stringent EMC and power filtering requirements mean engineers must carefully identify electrical noise intrusion to power and signal lines that require common-mode and differential-mode filtering. In common-mode noise, the signals on the two lines are in phase with each other. This is often seen in signals with a ground connection where a noise current is developed in the ground path due to a parasitic capacitance between the cable and the ground. Common-mode current can create high-level voltage spikes that damage electronics or create EMI. In this case, common-mode chokes are employed. Often composed of a toroidal ferrite core wrapped with two independent coils of the same size and number of turns, common-mode chokes are four-terminal components that essentially insert a large inductance in series with common-mode sources. This significantly impedes common-mode noise while having minimal effect on the desired signal. Eaton’s common-mode through-hole (ECMT) and common mode surface mount (ECMS) family of chokes are ideal for noise attenuation over a wide range of frequencies up to 100 megahertz while reducing board size. The ECMT’s feature a metallization on the ferrite core that results in excellent shock resistance and damage-free durability for operation from -40 °C to 125 °C. A closed magnetic circuit design reduces leakage flux and EMI, while the iron-based core provides a large saturation current. The ECMTs come in five through-hole sizes, offer inductance values up to 85 millihenries, and enable automated production with tray packaging. The ECMS are high frequency, magnetically shielded filters that come in three surface mount sizes and are footprint compatible with other commonly used common-mode chokes. With a low DC resistance and impedance values from 70 Ohms to 3,000 Ohms. These common chokes offer a high current capability of up to 15 Amps allowing for use in high-powered signal lines. Between the ECMT and ECMS, Eaton’s family of common-mode chokes offer a complete range of filtering options with high current ratings, a wide range of impedance values, and high inductance values.
