Summary of EMI interference sources for LED switching power supplies

LED switching power supplies are currently widely used in lighting, industry and communication fields. However, in the process of application and debugging, EMI interference is still one of the more common problems. So, where is the source of this kind of interference that causes headaches for engineers?

LED switching power supply is a popular switching power supply type in recent years. Once EMI interference occurs during the debugging process, the interference problem is mainly composed of internal and external parts. The internal interference is concentrated in the power switch tube, rectifier diode, high-frequency transformer and other components. The external environment interference mainly comes from the jitter of the power grid, lightning strikes, and external radiation. Next, we will analyze one by one.

First of all, let's look at the EMI interference problem caused by the power switch tube. During the operation of the LED power supply, the power switch tube works in the state of On-Off rapid cyclic conversion, and both dv/dt and di/dt are changing rapidly. Therefore, the power switch tube is not only the main source of interference for electric field coupling, but also the source of magnetic field coupling. main source of interference.

And high-frequency transformers will also produce large EMI interference problems. On the premise that the switching power supply is turned on, the EMI source of the high-frequency transformer is mainly reflected in the rapid cyclic transformation of di/dt corresponding to the leakage inductance.

The rectifier diode is also one of the problem parts that generate EMI interference internally. In the case of normal turn-on, the EMI source of the rectifier diode is concentrated in the reverse recovery characteristics. Stray inductances, etc. produce high dv/dt, resulting in strong EMI. In addition, the PCB is also one of the parts that cause EMI interference inside the switching power supply. To be precise, the PCB is the coupling channel of the above-mentioned interference sources. The quality of the PCB will directly correspond to the quality of the above-mentioned EMI source suppression. .