The Pulse Swarm Suppression Problem of Power Supply
Switching power supplies can be used separately as an electronic device, but more often than not, they are used as a component in conjunction with each electronic device. Therefore, switching power supplies have their own particularity, and the electromagnetic compatibility performance of switching power supplies is crucial for the normal use of every electronic device. Because of this, the electromagnetic compatibility performance of an electronic device depends first on the electromagnetic compatibility performance of the switching power supply.
① The Problem of Pulse Swarm Suppression in Switching Power Supplies
As for switching power supplies, aside from the input filters of switching power supplies, switching
The power supply circuit itself has a very low suppression effect on pulse group interference. The main reason for this is that the essence of pulse group interference is high-frequency common mode interference, while the filtering capacitors in the switching power supply circuit are set to suppress low-frequency differential mode interference. The electrolytic capacitors in the switching power supply circuit have insufficient ripple suppression effect on the switching power supply itself, Not to mention the suppression effect on pulse group interference with harmonic components above 60MHz, therefore, when observing the pulse group waveform of the input and output ends of the switching power supply with an oscilloscope, there is no obvious interference attenuation effect.
Considering that pulse group interference is a common mode interference.
For switching power supplies, using input filters is an important measure to suppress the pulse group interference received by the switching power supply.
Secondly, the design of high-frequency transformers in switching power supply circuits, especially the use of shielding measures, has a certain inhibitory effect on pulse group interference.
Furthermore, the bridging capacitance between the primary and secondary circuits of a switching power supply can provide a path for common mode interference from the primary circuit to return to the primary circuit, and also has a certain inhibitory effect on pulse group interference.
Finally, adding a common mode filter circuit (common mode inductor and common mode capacitor) at the output end of the switching power supply can also play a certain role in suppressing pulse group interference.
In addition, the switching power supply circuit itself has little inhibitory effect on pulse group interference, but if the circuit layout of the switching power supply is poor, it can further exacerbate the intrusion of pulse group interference into the switching power supply. Especially the essence of pulse group interference is the combination of conducted and radiated interference. Even though the use of input filters suppresses the components of conducted interference, the radiated interference that exists around the transmission line still exists. It can still penetrate the layout of the switching power supply (the primary or secondary circuit layout of the switching power supply is too open, forming a "large loop antenna") to induce the radiation components in pulse group interference, This in turn affects the anti-interference performance of the entire device.
② Regarding the pulse group suppression problem of switching power supplies, precautions should be taken in the pulse group test of equipment power supplies
When conducting pulse group anti-interference tests on the power side of electronic devices, we are certainly
Attention should be paid to the anti-interference performance of the equipment power supply, but we should not forget the fact that pulse group interference is essentially a combination of conduction and radiation interference. Therefore, when sufficient measures are taken on the power supply and the test still fails, it is necessary to consider whether interference can enter the equipment through other means, causing the false image of the equipment's power line pulse group immunity test failing.
