Welcome to the official website of Zhizhong Electronics Co., Ltd.Company focus: Ceramic Capacitor, Monolithic capacitor

     X, Y safety capacitors at the power input

     At the AC power input end, it is generally necessary to add three capacitors to suppress EMI conducted interference. The input of AC power can generally be divided into three wires: live wire (L) / change (N) / ground wire (G).
The capacitors connected in parallel between the live wire and the ground wire and between the neutral wire and the ground wire are generally called Y capacitors. The location of the connection of these two Y capacitors is critical and must comply with relevant safety standards to prevent leakage of electronic equipment or electrification of the housing
, It is easy to endanger personal safety and life, so they are all safety capacitors, and the capacitance value must not be too large, and the withstand voltage must be higher. Generally, the machine working in the subtropical zone requires the leakage current to the ground not to exceed 07mA; working in the temperate machine,
It is required that the leakage current to the ground cannot exceed 0.35mA. Therefore, the total capacity of Y capacitors generally cannot exceed 4700pF.

     Special reminder: Y capacitors are safety capacitors and must be certified by safety inspection agencies. The withstand voltage of Y capacitors is generally marked with a safety certification mark and AC250V or AC275V, but its real DC withstand voltage is as high as 5000V or more.
Therefore, Y capacitors cannot be replaced by ordinary capacitors such as nominal withstand voltage AC250V or DC400V.

    The capacitor connected in parallel between the live line and the neutral line suppression is generally called an X capacitor. Since the location of the capacitor connection is also critical, it also needs to comply with safety standards. Therefore, the X capacitor is also one of the safety capacitors.
The capacitance of the X capacitor is allowed to be larger than that of the Y capacitor, but a safety resistor must be connected in parallel at both ends of the X capacitor to prevent the power cord plug from being charged for a long time due to the charging and discharging process of the capacitor when the power cord is unplugged.
The safety standard stipulates that when the power cord of the working machine is unplugged, within two seconds, the charged voltage (or ground potential) at both ends of the power cord plug must be less than 30% of the original rated working voltage.
In the same way, X capacitors are also safety capacitors and must be certified by the safety inspection agency. The withstand voltage of X capacitors is generally marked with a safety certification mark and AC250V or AC275V, but its real DC withstand voltage is as high as 2000V or more.
Do not use ordinary capacitors such as AC250V or DC400V with nominal withstand voltage at will.

    X capacitors generally use polyester film capacitors with a relatively large ripple current. This type of capacitor is generally large in size, but its allowable instantaneous charging and discharging current is also large, and its internal resistance is correspondingly relatively high. small.
Ordinary capacitors have low ripple current indicators and high dynamic internal resistance. Using ordinary capacitors instead of X capacitors, in addition to the withstand voltage conditions can not be met, the general ripple current index is also difficult to meet the requirements.

    In fact, it is impossible to completely filter out conducted interference signals by only relying on Y capacitors and X capacitors. Because the frequency of the interference signal is very wide, basically covering tens of KHz to hundreds of MHz,
Even the frequency range of thousands of MHz. Usually a large capacity filter capacitor is required to filter low-end interference signals, but due to safety conditions, the capacity of the Y capacitor and the X capacitor cannot be used;
The filtering performance of large-capacity capacitors is extremely poor for filtering out terminal interference signals. In particular, the high-frequency performance of polyester film capacitors is generally poor, because it is produced by a winding process.
Moreover, the high-frequency response characteristics of polyester film dielectrics are far different from those of ceramic or mica. Generally, polyester film dielectrics have an adsorption effect, which will reduce the operating frequency of the capacitor. The operating frequency range of polyester film capacitors is about 1MHz.
The impedance will increase significantly above 1MHz.

    Therefore, in order to suppress the conduction interference generated by electronic equipment, in addition to the selection of Y capacitors and X capacitors, multiple types of inductance filters must be selected together to filter out the interference together.
Inductive filters are mostly low-pass filters, but inductive filters also have many specifications, such as differential mode, common mode, and high frequency and low frequency. Each type of inductance is mainly used to filter out interference signals of a certain frequency.
Then the distributed capacitance of the inductor is also very large. High-frequency interference signals will be bypassed by distributed capacitors. Moreover, the magnetic core with high permeability has a lower operating frequency. At present, most of the operating frequencies of magnetic cores of inductance filters that are widely used are below 75 MHz.
For fields with relatively high operating frequency requirements, high-frequency toroidal cores must be used. The permeability of high-frequency toroidal cores is generally not high, but the leakage inductance is particularly small, such as amorphous alloy cores, Permalloy box gold, etc.

Zhizhong Electronics Co., Ltd. has specialized in the production of safety, ceramic, and monolithic capacitors for 30 years. All staff will serve you wholeheartedly, please contact our online customer service or call our sales hotline 0769-88839201