What is a safety capacitor? What are its functions?

On the switching power supply, the safety capacitor is an essential electronic component under normal circumstances, but what role does the safety capacitor play in the switching power supply, I believe that many laymen do not really understand it, the editor will share it below On the switching power supply, what role does the safety capacitor play?​​

What is a safety capacitor?

The explanation for safety capacitors is: safety capacitors refer to safety capacitors that will not cause electric shock and endanger personal safety after the capacitor fails. In fact, it is not only used to protect the safety of our users, but also to the circuit. very important filter capacitors. The role of safety capacitors in switching power supplies has the following two points:

1. X safety capacitors, Z commonly used X2 safety capacitors, and some use X1 capacitors.​​

The X2 capacitor is mainly connected in parallel between the power grids, that is, between the live wire and the neutral wire of the wire. This capacitor can filter out the series mode interference (also called differential mode interference) between the grid lines. The higher the rated voltage of the X2 capacitor, the higher the rated voltage. The lowest in the industry is 275VAC, the medium is 310VAC, and the better rated voltage is 350/380VAC. The higher the rated voltage, the more margin, longer life and better filtering effect. .​​

2. Safety Y capacitors, Z commonly used are Y1 and Y2 safety capacitors.​​

The main function of the Y capacitor is to suppress common mode interference, which can filter out the common mode interference generated by the coupling capacitance of the primary winding and the secondary winding. The common terminal is used to filter out the high-frequency interference in the 10~200MHz frequency band, so it needs to be connected with a short lead. The common capacity range is 1~2.2nF The withstand voltage value is generally not less than 1.5kV.​​

Generally, on the switching power supply, X and Y capacitors need to be used together to protect the user's safety and EMC filtering.​​

Can switching power supply use safety capacitors?

In theory, it can be used even without safety capacitors, but the life of the power supply will be shortened (there may be abnormal pulse voltages such as lightning in the mains, which may cause the switched capacitors to be easily damaged), and the power supply itself also needs After passing the safety certification, if the safety capacitor is not used, the power supply itself cannot pass the safety regulation, so the safety capacitor on the switching power supply is essential.