Introduction to solving the problem of excessive radiation of switching power supply
The voltage and current change rates of switch mode power supplies are high, resulting in significant interference intensity; The interference sources are mainly concentrated during the power switch period and the connected heat sinks and high-level transformers, and their positions are relatively clear compared to the interference sources in digital circuits; The switching frequency is not high (ranging from tens of kilohertz to several megahertz), and the main forms of interference are conducted interference and near-field interference.
The specific solutions for exceeding the standard at each frequency point are as follows:
Within 1MHz:
Mainly based on differential mode interference: 1. Increase X capacity; 2. Add differential mode inductors; 3. Small power supplies can be processed using PI type filters (it is recommended to use larger electrolytic capacitors near transformers).
1M-5MHz：
Differential mode and common mode mixing, using an input terminal and a series of X capacitors to filter out differential interference and analyze which type of interference exceeds the standard and solve it;
5MHz：
The above mainly focuses on co touch interference and adopts the method of suppressing co touch. For the grounding of the shell, winding a magnetic ring twice on the ground wire will significantly attenuate interference above 10MHz (diudiu2006); For 25-30MHz, it is possible to increase the ground Y capacitor, cover the transformer with copper foil, change the PCBLAYOUT, connect a small magnetic ring with two wires wound in front of the output line at least 10 times, and install RC filters at both ends of the output rectifier tube.
1M-5MHZ：
Differential mode common mode mixing, using a series of X capacitors connected in parallel at the input end to filter out differential interference and analyze which type of interference exceeds the standard and solve it. 1. For differential interference exceeding the standard, adjust the X capacity, add differential mode inductors, and adjust the differential mode inductance; 2. For common mode interference exceeding the standard, common mode inductance can be added and a reasonable inductance can be selected to suppress it; 3. The characteristics of the rectifier diode can also be changed to handle a pair of fast diodes such as FR107 and a pair of ordinary rectifier diodes 1N4007.
Above 5MHz:
Mainly using co touch interference and adopting methods to suppress co touch.
For the grounding of the shell, winding a magnetic ring in series 2-3 times on the ground wire will have a significant attenuation effect on interference above 10MHz; You can choose to stick copper foil tightly to the iron core of the transformer and close the copper foil loop. Process the size of the absorption circuit of the backend output rectifier and the parallel capacitor of the primary circuit.
For 20M-30MHz:
For a certain type of product, adjusting the Y2 capacitance to ground or changing the Y2 capacitance position can be used;
2. Adjust the position and parameter values of the Y1 capacitor between the primary and secondary sides;
