In the EMC-related experiments of circuits, there are some voltage pulse experiments. How should the withstand voltage value of the capacitor be considered?

小太阳yy

In the EMC-related experiments of circuits, there are some voltage pulse experiments. How should the withstand voltage value of the capacitor be considered? [Copy link]

 

The figure shows the related voltage pulse experiment. It can be seen that in the 12V system, the highest US reaches -150V. So when we choose the input filter capacitor, should we choose the one with a withstand voltage of more than 150V?

In actual situations, a 50V withstand voltage is often selected, while the electrolytic capacitor may have an even lower withstand voltage, perhaps only 35V. Will this not cause damage to the filter capacitor?

zhangdaoyu

This may be related to the energy of the pulse, similar to static electricity. The voltage is very high, but the energy is actually very small. I don't know the specific theoretical support and I haven't paid attention to it.

maychang

Capacitors can withstand more abuse, but semiconductor devices, especially those using MOS technology, cannot.

chunyang

The withstand voltage of a capacitor only considers extreme conditions under normal operation. The high-voltage pulse energy of a pulse train test is very small, which is completely different from power supply.

小太阳yy

chunyang posted on 2022-3-30 19:14 The withstand voltage of capacitors only considers the extreme conditions under normal operation. The high-voltage pulse energy of the pulse train test is very small, which is completely different from power supply.

How should we understand this energy? Is the damage of capacitor due to high energy?

se7ens

The capacitor charging formula can solve your problem.

chunyang

Xiaoyangyy posted on 2022-3-31 19:15 How should we understand this energy? Is the damage of the capacitor due to the large energy?

The "energy" mentioned here refers to the amount of electricity charged into the capacitor, which determines the voltage across the capacitor. Overvoltage can break through the insulating medium of the capacitor and cause damage to the capacitor.

The relationship between capacitor capacity, the amount of charge charged and the voltage across the capacitor is U=Q/C, which was taught in high school physics class.

akii

This waveform seems to be the ISO7637 Pulse-1 waveform?

小太阳yy

chunyang posted on 2022-4-1 13:15 The "energy" here refers to the amount of electricity charged into the capacitor, which determines the voltage across the capacitor. Overvoltage breakdown of the insulating medium of the capacitor can cause electric...

I understand what you mean. It is the same as absorbing static electricity.