Pulse group suppression problem of switching power supply
The switching power supply can be used alone as an electronic device, but more often the switching power supply is used as a component with each electronic device. Therefore, the switching power supply has its particularity. The electromagnetic compatibility performance of the switching power supply is related to 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 Pulse group suppression problem of switching power supply
As far as switching power supplies are concerned, leaving aside the input filter of the switching power supply, the switching power supply
The power supply line itself has a very low suppression effect on pulse group interference. The main reason is that the essence of pulse group interference is high-frequency common mode interference, and the filter capacitors in switching power supply lines are designed to suppress low-frequency differential mode interference. However, the electrolytic capacitor is not enough to suppress the ripple of the switching power supply itself, let alone suppress the pulse group interference with harmonic components above 60MHz. Therefore, use an oscilloscope to observe the input and output of the switching power supply. When the pulse group waveform is at the end, no obvious interference attenuation effect can be seen.
Consider that burst interference is interference of a common mode nature.
As far as switching power supplies are concerned, the use of input filters is an important measure for the switching power supply to suppress pulse group interference.
Secondly, the design of the high-frequency transformer in the switching power supply line, especially the use of shielding measures, has a certain inhibitory effect on pulse group interference.
Furthermore, the cross-connect capacitance between the primary circuit and the secondary circuit of the switching power supply can provide a path for the common mode interference from the primary circuit to the secondary circuit to return to the primary circuit, which is
It also has a certain inhibitory effect on pulse group interference.
Finally, adding a common-mode filter circuit (common-mode inductor and common-mode capacitor) to 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 no inhibitory effect on pulse group interference, but if the circuit layout of the switching power supply is poor, it will further intensify the intrusion of pulse group interference into the switching power supply. In particular, the essence of pulse burst interference is a combination of conduction and radiation interference. Even if the conduction interference component is suppressed due to the use of an input filter, the radiation interference that exists around the transmission line still exists, and the switching power supply can still be transmitted. 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"), induces radiation components in pulse group interference
② Regarding the pulse group suppression problem of switching power supply, what should be paid attention to during the pulse group test of equipment power supply
When conducting pulse group anti-interference tests on the power supply side of electronic equipment, we certainly
We should pay attention to the anti-interference performance of the equipment power supply, but we should not forget the fact that pulse burst interference is essentially a combination of conduction and radiation interference. Therefore, if the power supply part still fails to pass this test after taking sufficient measures, it should be replaced. I wonder if interference may enter the equipment through other means, causing the equipment's power line pulse group immunity test to fail.
