From three aspects of the switching power supply to talk about electromagnetic interference suppression methods
1, suppression of various sources of electromagnetic interference in the switching power supply
In order to solve the input current waveform distortion, reduce the current harmonic content, switching power supply needs to use power factor correction (PFC) technology. pfc technology makes the current waveform follow the voltage waveform, correct the current waveform so that it is close to a sinusoidal waveform. This reduces the current harmonic content, improves the input characteristics of the bridge rectifier capacitor filter circuit, and improves the power factor of the switching power supply. Different methods can inhibit electromagnetic interference from different perspectives, and Minmelt Electric has made a lot of technical inputs and paid a lot of effort to this end. Minmelt switching power supply in the electromagnetic interference suppression has not low results, Minmelt Electric's efforts, casting the Minmelt switching power supply in the industry more and more giant position.
Soft switching technology is an important means to reduce switching device losses and improve the electromagnetic compatibility of switching devices. Switching devices in the switching process will produce inrush current and spike voltage, which is the main cause of electromagnetic interference and switching losses. The use of soft switching technology so that the switching tube at zero voltage, zero current switching conversion can effectively suppress electromagnetic interference. The use of buffer circuits to absorb the spike voltage of the primary coil of the switching tube or high-frequency transformer can also effectively improve the electromagnetic compatibility characteristics.
The reverse recovery problem of the output rectifier diode can be suppressed by series connection of saturated inductors. The core of a saturable inductor is made of a magnetic material with a rectangular BH curve. As with materials used in magnetic amplifiers, inductors made from such cores have a high permeability. The core has a near-vertical linear region on the BH curve and easily goes into saturation. In practice, when the output rectifier diode is on, the saturation inductor operates in an inductive characteristic state, which is equivalent to a piece of wire; when the diode is off and recovered in reverse, the saturation inductor is in an inductive characteristic state, which suppresses the large change in the reverse recovery current and suppresses its external interference.
2, cut off the transmission path of electromagnetic interference - common mode and differential mode power line filter design
Power line filter can filter out power line interference. A reasonable and effective switching power supply EMI filter must have a strong inhibition of both differential mode interference and common mode interference. In fact, not only the power line filter, Minfong Electric has also developed the means to suppress EMI in some specific components, and the user experience is one of the directions that Minfong Electric insists on. The technological development of Minfong Electric is inseparable from the direction that Minfong Electric insists on, which makes Minfong switching power supply gradually achieve the quality of craftsmanship.
Common mode inductor consists of two windings with opposite direction and same number of turns on the same magnetic ring. Generally use ring core, small leakage, high efficiency, but difficult to wind. When the utility network frequency current flows through the two windings, is one in one out, the magnetic field generated just to offset, so that the common mode inductor will not hinder the utility network frequency current, and can be transmitted without loss. If there is a common-mode noise current in the utility network through the common-mode inductor, the common-mode noise current is in the same direction. When it flows through the two windings, the magnetic field generated in the same phase superposition, so that the common mode inductor on the interference current shows a greater inductive resistance, play a role in suppressing common mode interference.
3, the use of shielding to reduce the sensitivity of electromagnetic sensitive equipment
Shielding is an effective way to suppress radiated noise. Good conductivity materials can be used to shield the electric field, high permeability materials can be used to shield the magnetic field. In order to prevent the transformer leakage field, so that the primary coupling is good, closed magnetic ring can be used to form a magnetic shield. For example, the leakage flux of a can-type core is much smaller than that of an e-type core. The connecting and power cables of switching power supplies should be made of conductors with a shield to prevent external interference from coupling into the circuit. Or use magnetic beads, magnetic rings and other EMC components to filter out high-frequency interference from the power supply and signal lines. However, it should be noted that the signal frequency should not be interfered by EMC components, i.e. the signal frequency should be within the filter. The entire switching power supply enclosure also needs to have good shielding characteristics, and the connectors should meet the shielding requirements specified by EMC. The above measures ensure that the switching power supply is not subject to interference from the external electromagnetic environment and does not interfere with external electronic equipment.
1, suppression of various sources of electromagnetic interference in the switching power supply
In order to solve the input current waveform distortion, reduce the current harmonic content, switching power supply needs to use power factor correction (PFC) technology. pfc technology makes the current waveform follow the voltage waveform, correct the current waveform so that it is close to a sinusoidal waveform. This reduces the current harmonic content, improves the input characteristics of the bridge rectifier capacitor filter circuit, and improves the power factor of the switching power supply. Different methods can inhibit electromagnetic interference from different perspectives, and Minmelt Electric has made a lot of technical inputs and paid a lot of effort to this end. Minmelt switching power supply in the electromagnetic interference suppression has not low results, Minmelt Electric's efforts, casting the Minmelt switching power supply in the industry more and more giant position.
Soft switching technology is an important means to reduce switching device losses and improve the electromagnetic compatibility of switching devices. Switching devices in the switching process will produce inrush current and spike voltage, which is the main cause of electromagnetic interference and switching losses. The use of soft switching technology so that the switching tube at zero voltage, zero current switching conversion can effectively suppress electromagnetic interference. The use of buffer circuits to absorb the spike voltage of the primary coil of the switching tube or high-frequency transformer can also effectively improve the electromagnetic compatibility characteristics.
The reverse recovery problem of the output rectifier diode can be suppressed by series connection of saturated inductors. The core of a saturable inductor is made of a magnetic material with a rectangular BH curve. As with materials used in magnetic amplifiers, inductors made from such cores have a high permeability. The core has a near-vertical linear region on the BH curve and easily goes into saturation. In practice, when the output rectifier diode is on, the saturation inductor operates in an inductive characteristic state, which is equivalent to a piece of wire; when the diode is off and recovered in reverse, the saturation inductor is in an inductive characteristic state, which suppresses the large change in the reverse recovery current and suppresses its external interference.
2, cut off the transmission path of electromagnetic interference - common mode and differential mode power line filter design
Power line filter can filter out power line interference. A reasonable and effective switching power supply EMI filter must have a strong inhibition of both differential mode interference and common mode interference. In fact, not only the power line filter, Minfong Electric has also developed the means to suppress EMI in some specific components, and the user experience is one of the directions that Minfong Electric insists on. The technological development of Minfong Electric is inseparable from the direction that Minfong Electric insists on, which makes Minfong switching power supply gradually achieve the quality of craftsmanship.
Common mode inductor consists of two windings with opposite direction and same number of turns on the same magnetic ring. Generally use ring core, small leakage, high efficiency, but difficult to wind. When the utility network frequency current flows through the two windings, is one in one out, the magnetic field generated just to offset, so that the common mode inductor will not hinder the utility network frequency current, and can be transmitted without loss. If there is a common-mode noise current in the utility network through the common-mode inductor, the common-mode noise current is in the same direction. When it flows through the two windings, the magnetic field generated in the same phase superposition, so that the common mode inductor on the interference current shows a greater inductive resistance, play a role in suppressing common mode interference.
3, the use of shielding to reduce the sensitivity of electromagnetic sensitive equipment
Shielding is an effective way to suppress radiated noise. Good conductivity materials can be used to shield the electric field, high permeability materials can be used to shield the magnetic field. In order to prevent the transformer leakage field, so that the primary coupling is good, closed magnetic ring can be used to form a magnetic shield. For example, the leakage flux of a can-type core is much smaller than that of an e-type core. The connecting and power cables of switching power supplies should be made of conductors with a shield to prevent external interference from coupling into the circuit. Or use magnetic beads, magnetic rings and other EMC components to filter out high-frequency interference from the power supply and signal lines. However, it should be noted that the signal frequency should not be interfered by EMC components, i.e. the signal frequency should be within the filter. The entire switching power supply enclosure also needs to have good shielding characteristics, and the connectors should meet the shielding requirements specified by EMC. The above measures ensure that the switching power supply is not subject to interference from the external electromagnetic environment and does not interfere with external electronic equipment.
