
使用 MOSA、SOSA 和 VPX 開放式架構的標準化防禦平臺的未來
使用開放標準化電子系統以提高互操作性、可擴充性、可靠性,降低系統成本,並儘量減少定制電子設計數量
EMI is seen as one of the key challenges of power conversion design and system integration, particularly for AC-DC systems. Our latest technical tip by David Fletcher, Principal Engineer from Vicor’s Westcor Division, looks at the causes of EMI and its impact on a system, before going on to make some practical suggestions on how to minimize its effect.
We have to start with what engineers affectionately call noise. This is generated whenever rapid voltage (dv/dt) and/or current (di/dt) transitions take place. AC-DC power converters typically utilize a number of power switching topologies, including fully resonant, quasi-resonant and PWM (Pulse Width Modulation), the most typical control in the front-end section of the converter.
PWM-controlled converters use a rectangular control signal with a continuously varying pulse width in response to the operating conditions of the converter. The result is typically a “white noise” energy distribution spectrum. If this was not filtered and shielded it would interfere with consumer electronic equipment using the same AC mains.
“Noise” currents exiting the power converter through the AC power lines and/or via output power cables are known as “conducted emissions.” The noise manifests itself in two forms: differential and common-mode. The definition of differential-mode is noise that is only on the power lines and is not present on the earth ground lead, and can be measured with respect to the power lines. The definition of common-mode is noise that can only be measured from earth ground to one of the power lines.
AC-DC power converters employ EMI filters within the power converter enclosure. These filters contain noise suppression topologies containing inductive and capacitive components. These components are called “X” and “Y” elements. The “X” components are placed across the power lines and filter the differential-mode noise; the “Y” components are placed between the power lines and earth ground and filter common-mode noise.
AC-DC power converters are designed to meet various regulatory and safety standards, including various EMI standards. The individual details and the standards met are generally covered thoroughly in the product literature. However, during a system integration of various components, including an AC-DC power converter, a system design engineer may find it necessary to add additional EMI filtering to enable the integrated system to comply with all relevant agency standards. If this approach becomes necessary, it is recommended to minimize the additional filter components required by empirically gathering test information. It is recommended that a few areas be given special attention:
If EMI problems still persist, then adding an external filter may be necessary. There are areas to consider when considering an off-the-shelf filter:
使用 MOSA、SOSA 和 VPX 開放式架構的標準化防禦平臺的未來
使用開放標準化電子系統以提高互操作性、可擴充性、可靠性,降低系統成本,並儘量減少定制電子設計數量
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