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Switching power supply EMC generation mechanism and its countermeasures

  • Categories:Industry News
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  • Time of issue:2024-11-07
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Switching power supply EMC generation mechanism and its countermeasures

  • Categories:Industry News
  • Author:
  • Origin:
  • Time of issue:2024-11-07
  • Views:0

As an indispensable energy conversion device in modern electronic equipment, switching power supply has the advantages of high efficiency, small size and light weight. However, switching power supply in the working process will produce electromagnetic interference (Electromagnetic Interference, EMI), which not only affects its own Electromagnetic Compatibility (Electromagnetic Compatibility, EMC), but also may cause interference to other electronic equipment. Therefore, in-depth discussion of switching power supply EMC generation mechanism, and put forward effective countermeasures, to enhance the overall performance and stability of electronic equipment is of great significance.

 

The working principle of switching power supply and EMC issues
The core of switching power supply is to realize the conversion and transmission of energy through high-frequency switching action. Specifically, the switching power supply converts the input AC voltage into a high-frequency pulse signal through the fast switching of the switching tubes, and then through the transformation of the transformer or inductor and the processing of the filtering circuit, and finally outputs a stable DC voltage. This high-frequency switching mode of operation brings high efficiency, but also for the generation of EMC interference laid the foundation.

 

EMC interference generation mechanism
Switching power supply EMC interference generated by a variety of complex reasons, mainly including the following aspects:
High-frequency switching currents and voltages: switching elements in switching power supplies (such as transistors, MOSFETs, etc.) operate at high frequencies (usually in the tens of kilohertz to hundreds of kilohertz) for switching operations, and these fast switches produce steep current and voltage waveforms that contain abundant high-frequency harmonic components. These harmonics are radiated through the power lines, power enclosures, and connecting cables, causing interference to surrounding electronic equipment.
Parasitic parameters: All electronic components have a certain amount of parasitic inductance, capacitance and resistance. During high-frequency switching, these parasitic parameters interact with the switching elements to form oscillating circuits that generate high-frequency oscillations. These oscillating signals will also generate external interference by radiation or conduction.
Diode reverse recovery: In switching power supplies, diodes are commonly used for rectification and current continuation. When the diode from the conduction state to the cut-off state, will undergo a period of reverse recovery process, the process of redistribution of the charge inside the diode, may produce a large transient current, which in turn triggers electromagnetic interference.
Switching joints of the voltage jump: switching power supply switching joints in the switching process will experience rapid voltage changes, these voltage jumps can be regarded as the source of electromagnetic interference, through the power supply internal wiring, PCB alignment, etc. to the outside world to radiate electromagnetic waves.
Power supply layout and wiring: unreasonable power supply layout and wiring is also an important source of EMC interference. For example, high power switching nodes are too close to sensitive signal lines, or proper shielding measures are not taken, which can lead to the generation and propagation of electromagnetic interference.

 

Countermeasures to suppress EMC interference
For the EMC interference generated by switching power supply, a variety of measures can be taken to suppress, mainly including filtering technology, shielding technology, grounding technology and wiring optimization:
Filtering technology: The use of suitable filters to suppress high-frequency noise is an effective means of reducing EMC interference. Filters can be placed at the input and output, respectively, to filter out conducted and radiated interference.
Shielding techniques: Designing suitable shielding structures and shielding materials to reduce electromagnetic radiation. For example, use metal shielding to cover the key components of the switching power supply, or use shielding in the PCB layout to isolate sensitive circuits and sources of interference.
Grounding technology: Control the grounding of equipment to ensure a good ground connection. Reasonable grounding design can reduce the impedance of the ground loop, reduce common mode interference, while improving the electromagnetic compatibility of the system.
Wiring Optimization: Optimize the wiring of power and signal lines to reduce crossover and coupling. Avoid long and thin wires to reduce electromagnetic radiation and interference from sensitive equipment. At the same time, control the wiring paths of signal and power lines to reduce interference crossings and coupling.
Use low-noise components: Select low-noise switching components, filters and rectifier diodes, etc., to reduce the generation of electromagnetic interference from the source.
Electromagnetic compatibility simulation and testing: carry out electromagnetic compatibility simulation and testing at the design stage to find and solve problems in time. Evaluate the EMC performance of the switching power supply by simulating the real electromagnetic environment and optimize the design according to the test results.
Comply with relevant standards and norms: Comply with relevant EMC standards and norms to ensure that the products meet the requirements. This not only improves the market competitiveness of the product, but also avoids legal disputes and economic losses caused by electromagnetic interference problems.

 

Specific case study
Taking the switching power supply with Flyback architecture as an example, the EMI generated by it has specific characteristics in terms of its response on the frequency spectrum. For example, the oscillation generated at 0.15MHz is the interference caused by the 3rd harmonic of the switching frequency; the oscillation generated at 0.2MHz is the interference caused by the 4th harmonic of the switching frequency and the iteration of the fundamental wave of the MOSFET oscillation2. Through spectrum analysis, the main sources of interference can be identified and appropriate suppression measures can be taken.
In the Flyback architecture, EMI can be reduced by optimizing the transformer winding, adding absorption circuits, and reducing leakage inductance, etc. In addition, a series of measures can be taken in the PCB design, such as reducing the area of PCB copper foil at the noisy circuit nodes, keeping the inputs and outputs away from the noisy components, and keeping the EMI filters far away from the power transformer.

 

Conclusion
The EMC interference problem of switching power supply is a complex and important subject. By deeply understanding the working principle of switching power supply and the mechanism of EMC interference generation, and taking effective suppression measures, we can significantly reduce the impact of electromagnetic interference of switching power supply on the environment and other electronic equipment, and improve the stability and reliability of the whole system. With the continuous development of electronic technology, the EMC performance requirements for switching power supplies will become higher and higher, so it is of great significance to continuously research and explore new suppression methods and techniques.

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