Discussion on Electromagnetic Interference Suppression Methods of Switching Power Supplies from Three Major Aspects
There are five sources of electromagnetic interference in switching power supplies, and the three elements of electromagnetic compatibility are interference sources, coupling paths, and sensitive bodies. Suppressing any of the above can reduce electromagnetic interference. The electromagnetic compatibility problem of switching power supply is more complex when it operates in a high-voltage, high current, and high-frequency switching state. However, it still conforms to the basic model of electromagnetic interference, and what are the methods for suppressing electromagnetic interference? Let's talk about electromagnetic interference suppression methods from three aspects in the small classroom.
1. Suppressing Various Electromagnetic Interference Sources in Switching Power Supplies
In order to solve the distortion of input current waveform and reduce the harmonic content of current, the switching power supply needs to use power factor correction (PFC) technology. PFC technology allows the current waveform to follow the voltage waveform, correcting the current waveform to approach a sine wave. Thus, the harmonic content of the current is reduced, the input characteristics of the bridge rectifier capacitor filter circuit are improved, and the power factor of the switching power supply is increased. Different methods can suppress electromagnetic interference from different perspectives, and Minrong Electric has invested a lot of technology and effort in this regard. Minrong Switching Power Supply has achieved significant results in electromagnetic interference suppression, and Minrong Electric's efforts have cast Minrong Switching Power Supply into an increasingly dominant position in the industry.
Soft switching technology is an important means to reduce switching device losses and improve electromagnetic compatibility of switching devices. Switching devices generate surge currents and peak voltages during the switching process, which are the main causes of electromagnetic interference and switching losses. The use of soft switching technology to switch the transistor at zero voltage and zero current can effectively suppress electromagnetic interference. The use of buffer circuits to absorb the peak voltage at both ends of the switch tube or high-frequency transformer primary coil can also effectively improve electromagnetic compatibility characteristics.
The reverse recovery problem of the output rectifier diode can be suppressed by serializing a saturated inductor. The core of a saturated inductor is made of magnetic material with a rectangular BH curve. Like the materials used in magnetic amplifiers, the inductance made of this magnetic core has high magnetic permeability. The magnetic core has a nearly vertical linear region on the BH curve, making it easy to enter a saturated state. In practical applications, when the output rectifier diode is on, the saturated inductor operates in the inductance characteristic state, equivalent to a section of wire; When the diode is turned off and reverse recovered, the saturated inductance is in the inductance characteristic state, which suppresses the significant change in reverse recovery current and external interference.
2. Cutting off the Transmission Path of Electromagnetic Interference - Design of Common Mode and Differential Mode Power Line Filters
The power line filter can filter out power line interference. A reasonable and effective EMI filter for switching power supply must have strong suppression effects on both differential mode interference and common mode interference. Actually, it's not just about power line filters. Minrong Electric has also developed methods to suppress electromagnetic interference on certain components, and user experience is one of the directions Minrong Electric adheres to. The technological development of Minrong Electric cannot be separated from its unwavering direction, which has gradually led to the achievement of craftsmanship quality in Minrong Switching Power Supply.
The common mode inductance is composed of two windings on the same magnetic ring with opposite directions and the same number of turns. Generally, circular magnetic cores are used, with low magnetic leakage and high efficiency, but winding is difficult. When the power frequency current of the city network flows through two windings, it is one in and one out, and the generated magnetic field precisely offsets it. This way, the common mode inductance will not hinder the power frequency current of the city network, and can be transmitted without loss. If there is a common mode noise current passing through the common mode inductance in the city network, the direction of the common mode noise current is the same. When it flows through two windings, the generated magnetic field is superimposed on the same phase, causing the common mode inductance to exhibit a greater inductive reactance towards the interference current, which plays a role in suppressing common mode interference.
3. Using Shielding to Reduce the Sensitivity of Electromagnetic Sensitive Equipment
Shielding is an effective way to suppress radiated noise. Materials with good conductivity can be used to shield electric fields, while materials with high magnetic permeability can be used to shield magnetic fields. To prevent transformer magnetic field leakage and ensure good primary coupling, a closed magnetic ring can be used to form a magnetic shield. For example, the leakage flux of the can type magnetic core is much smaller than that of the e-type core. The connecting wires and power lines of the switching power supply should use conductors with shielding layers to prevent external interference from coupling into the circuit. Alternatively, EMC components such as magnetic beads and rings can be used to filter out high-frequency interference from power and signal lines. However, it should be noted that the signal frequency should not be interfered by electromagnetic compatibility components, that is, the signal frequency should be within the filter. The entire shell of the switching power supply also needs to have good shielding characteristics, and the joints should meet the shielding requirements specified by EMC. By taking the above measures, ensure that the switching power supply is not affected by external electromagnetic environment interference and will not cause interference with external electronic devices.
