Pulse group suppression of switching power supply
Switching power supply can be used as an electronic device alone, but more often, switching power supply is used as a component with each electronic device. Therefore, switching power supply has its particularity, and the electromagnetic compatibility of switching power supply is related to the normal use of every electronic device. Because of this, the EMC performance of an electronic device depends on the EMC performance of the switching power supply first.
① Pulse group suppression of switching power supply.
As far as switching power supply is concerned, regardless of the input filter of switching power supply, the switch
The suppression effect of power supply circuit itself on burst interference is really very low. The main reason is that the essence of burst interference is high-frequency common-mode interference, and the filter capacitors in switching power supply circuit are all set to suppress low-frequency differential-mode interference. The electrolytic capacitors are not enough to suppress the ripple of switching power supply itself, let alone the pulse burst interference with harmonic components above 60MHz. Therefore, when observing the pulse burst waveforms at the input and output of switching power supply with oscilloscope, there is no obvious effect.
Considering that burst interference is common-mode interference.
As far as switching power supply is concerned, adopting input filter is the first important measure to suppress the pulse group interference suffered by switching power supply.
Secondly, the design of high-frequency transformer in switching power supply line, especially the adoption of shielding measures, has a certain inhibitory effect on pulse group interference.
Furthermore, the bridge capacitor between the primary circuit and the secondary circuit of the switching power supply can provide a path for the common-mode interference that enters the secondary circuit from the primary circuit to return to the primary circuit, which is right.
It also has a certain inhibitory effect on pulse group interference.
Finally, adding a common-mode filter circuit (common mode choke and common-mode capacitor) at the output of the switching power supply can also play a certain role in suppressing the burst interference.
In addition, the switching power supply circuit itself has no inhibitory effect on the burst interference, but if the circuit layout of the switching power supply is not good, it will aggravate the intrusion of the burst interference into the switching power supply. Especially, the essence of burst interference is the combination of conduction and radiation interference. Even if the conduction interference component is suppressed due to the adoption of the input filter, the radiation interference around the transmission line still exists, and it is still possible to induce the radiation component in the burst interference through the layout of the switching power supply (the primary or secondary circuit layout of the switching power supply is too open, forming a "big loop antenna"), thus affecting the anti-interference performance of the whole equipment.
(2) About the pulse burst suppression of switching power supply, what should be paid attention to in the pulse burst test of equipment power supply.
When the pulse group anti-interference test on the power supply side of electronic equipment is carried out, we certainly
Attention should be paid to the anti-interference performance of the power supply of the equipment, but we should not forget the fact that the essence of burst interference is the combination of conduction and radiation interference. Therefore, when the power supply part still fails to pass this test after taking adequate measures, we should put ourselves in another's shoes and think about whether the interference will enter the equipment through other means, causing the false image that the power supply line burst immunity test of the equipment is unqualified.
For example, when we do the pulse group immunity test of the power line, we are actually in electricity
There is a high-frequency radiated electromagnetic field with a certain intensity in the space around the source line. If the equipment has other communication and input/output connections besides the power line, it is still possible to accept the induction of high-frequency electromagnetic field through the passive antenna function of these lines and introduce it into the equipment. In addition, when the internal wiring of the equipment is too close to the casing; The equipment adopts a non-metallic casing; Or the electromagnetic tightness of the enclosure near the wiring is not good, it is also possible to induce the high-frequency radiation electromagnetic field generated by pulse group interference, resulting in unqualified immunity test of the equipment.
