Electromagnetic interference caused by the switch power supply circuit.

The circuit is the most basic element for maintaining the operation of the switch power supply. Therefore, for the switch power supply, the electromagnetic interference caused by the switch circuit is a source of interference within the switch power supply, and its impact on the switch power supply is significant, potentially causing serious damage. As the core of the switch power supply, the main components include the switch tube and high-frequency transformer. The quality of these two main components also greatly affects the switch circuit, making the quality of the switch tube and high-frequency transformer extremely important in the switch circuit.

As an important component of the switch power supply, the various types of interference it causes are also multifaceted, with diverse causes. Therefore, the causes need to be analyzed from different aspects. In this article, we will analyze in detail from the following aspects:

1. Switch tube load. The widespread application of switch tube load in China is the use of the primary coil of the high-frequency transformer, which belongs to the realm of resistive load. Moreover, at the moment the switch tube operates, the primary coil generates a large inrush current, resulting in a high surge peak voltage at both ends. Additionally, at the moment the switch tube turns off, due to the characteristics of the primary coil, some energy cannot be transferred from one coil to the second coil, leading to energy loss and thus causing a power interruption. The interruption of the power supply voltage generates a magnetization impact current around it, and this noise will be transmitted to the input and output terminals, causing conducted interference, and in severe cases, it may even break down the switch tube, directly causing the switch power supply to collapse.

2. The high-frequency switching current loop formed by the switch tube of the primary coil of the pulse transformer and the filter capacitor may generate significant spatial radiation, causing radiated interference. Similarly, the high-frequency impedance on the capacitor can lead to high-frequency circuits being conducted into the AC power supply in a differential mode, resulting in conducted interference.

Electromagnetic interference generated by the diode rectifier circuit of the switch power supply.

The reverse recovery current generated by the rectifier diode in the main circuit of the switch power supply differs from the reverse recovery current of the freewheeling diode. Generally speaking, the reverse recovery current generated by the rectifier diode in the main circuit is smaller, which actually enhances the level of electromagnetic interference of the switch power supply. According to relevant survey results, the small value of the reverse recovery current generated by the rectifier diode in the main circuit leads to a greater interference intensity and a wider frequency band. Additionally, the voltage jump generated by the rectifier diode in the main circuit is also smaller compared to other components, which similarly leads to more severe electromagnetic interference generated by the diode rectifier circuit, affecting the normal operation of the switch power supply.