Why Shouldn't the Capacitance of Y Capacitors Too Large

Safety capacitors are divided into X capacitors and Y capacitors. They are often used together in the power supply section, that is, the yellow box electronic components and blue components commonly found in power supplies.

The X capacitor and the Y capacitor are not distinguished by the material of the capacitor, but by the position in the power supply circuit. According to the peak pulse voltage across the Y capacitor, the Y capacitor is divided into three grades: Y1 capacitor, Y2 capacitor, and Y3 capacitor. The Y3 capacitor usually has no specific parameters.

Y1 capacitor: high voltage resistance value> 8 kV;

Y2 capacitor: 5kV < high voltage resistance < less than 8 kV;

Y3 capacitor: 2.5 kV < high voltage resistance < less than 5 kV.

Why should Y capacitors be distinguished between these three levels? This is because when designing the circuit, it is necessary to select a Y capacitor with a suitable withstand voltage value according to the peak voltage in the power supply circuit. If the selected Y capacitor grade is not enough or the withstand voltage value is lower than the peak voltage of the power supply circuit, the Y capacitor will not be able to play the protective role.

Why Can't The Capacitance of The Y Capacitor Be Too Large?

In the front-end circuit of the switching power supply, the Y capacitor is usually connected to the two capacitors between the primary and the secondary side of the circuit, and can provide a return path for the interference current coupled from the primary side to the secondary side, which plays a role as EMC, and in EMC, the important parameter of capacitance is leakage current.

What is leakage current? In the EMI circuit, the switching power supply has a small current after being powered on, which is the leakage current. The leakage current is harmful to the human body, and the human body will feel numb when it touches the small leakage current. If the leakage current is too large, the human body will be injured or killed, and electronic products and electronic equipment will be damaged.

There is a formula for leakage current as I=2πfCU. Among them: f is the mains frequency, that is, 50Hz; C is the total capacitance of the Y capacitor, and U is the voltage to the ground terminal. From the formula, the leakage current is proportional to the capacitance of the Y capacitor. The larger the capacitance of the Y capacitor, the greater the leakage current. For electrical appliances powered by 220V/50Hz AC grid, many regions stipulate that the leakage current should not be greater than 1mA, and the leakage current is proportional to the capacitance of the Y capacitor , which is why the capacitance of the Y capacitor in the power circuit should not be too large.

JYH HSU(JEC) Electronics Ltd (or Dongguan Zhixu Electronic Co., Ltd.) is one of largest manufacturers in China in terms of yearly safety capacitor (X2, Y1, Y2) production. Our factories are ISO 9000 and ISO 14000 certified. If you're looking for electronic components, welcome to visit our official website: https://www.jeccapacitor.com