Pulse grouping suppression problem of switching power supply
① The problem of pulse group suppression in switching power supply
As for switch mode power supplies, aside from the input filter of the switch mode power supply, the switch
The suppression effect of the power line itself on pulse group interference is very low. The main reason is that the essence of pulse group interference is high-frequency common mode interference, and the filtering capacitors in the switching power supply line are designed to suppress low-frequency differential mode interference. The electrolytic capacitors in the switching power supply have insufficient ripple suppression effect on the switching power supply itself, let alone suppression effect on pulse group interference with harmonic components above 60MHz. Therefore, when observing the pulse group waveforms at the input and output terminals 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 switch mode power supplies, using an input filter suppresses the pulse group interference that the switch mode power supply experiences
The first important measure of disturbance.
Secondly, the quality of the high-frequency transformer design in the switching power supply circuit, especially the adoption of shielding measures, has a certain inhibitory effect on pulse group interference.
Furthermore, the cross capacitor between the primary and secondary circuits of the switching power supply can provide a pathway for common mode interference entering the secondary circuit from the primary circuit to return to the primary circuit
It also has a certain inhibitory effect on pulse group interference.
Finally, adding a common mode filtering circuit (common mode inductor and common mode capacitor) at the output 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 invasion 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 if the components of conducted interference are suppressed due to the use of input filters, radiated interference still exists around the transmission line. 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"), induce the radiated components in pulse group interference, and thus affect the anti-interference performance of the entire device.
