Transient interference of power supply and its suppression

       A common type of interference noise is transient pulse interference noise. The characteristics of this type of interference noise are: large amplitude, short time, and wide frequency spectrum, which are more harmful to equipment. To solve this kind of interference, we need to use some special devices. Not only that, the power supplies we talk about are all switching power supplies, and their components are all working in the on-off state, and internal compatibility should also be paid attention to.

       1. Transient interference. Refers to electromagnetic interference with a short time but a large amplitude. There are three common transient interferences (devices need to pass a surge test to verify their immunity): electrical fast transient pulse group (EFT), surge, electrostatic discharge (ESD).

       2. Electrical fast transient pulse group. It is generated when the inductive load in the circuit is disconnected or generated by the switching circuit. Its characteristic is: it is not a single pulse, but a series of pulses, therefore, it has a greater impact on the circuit, and the test group pulse generator simulates the test. Because a series of pulses can produce a cumulative effect at the input of the circuit, the amplitude of the interference level will eventually exceed the noise threshold of the circuit. From the point of view of this mechanism, the shorter the period of the pulse train, the greater the impact on the circuit. Because, when each pulse in the pulse train is very close, the input capacitance of the circuit does not have enough time to discharge, and a new charge is started, which is easy to reach a higher level.

       3. Surge. Surge is mainly induced by lightning on the cable, and a switch with a large power can also generate a surge. The surge is characterized by high energy. Although surges are not as common as EFT, once they occur, the damage is very serious and often leads to circuit damage.

       4. Electrostatic discharge. The lightning phenomenon is actually a kind of electrostatic discharge phenomenon, and its impact on equipment cables has been reflected in the surge test. Another major phenomenon in the actual environment is electrostatic discharge when the human body touches the equipment. However, some standards have added device discharges that are more severe than human body discharges. The impact of these electrostatic discharges on the equipment is essentially radiated interference.