Why some Y capacitor is very small, and some Y capacitor is very large?
To charge the power cord for long periods of time. The safety standard stipulates that the voltage (or ground potential) charged at both ends of the power cord plug must be less than 30% of the original rated operating voltage within two seconds when the machine power cord is in operation.
In line between the line of fire and zero line suppression capacitor, commonly known as X capacitance. As the location of the capacitor connection is also more critical, the same need to meet the relevant safety standards. X capacitance is also one of the safety capacitors. According to the actual needs, the capacitance value of the X capacitor is larger than the capacitance of the Y capacitor. However, it is necessary to connect a safety resistor in parallel with the X capacitor to prevent the charging and discharging of the power supply line.
As a capacitor of the Y capacitor, it is required to obtain the certification of the safety inspection mechanism. Y capacitor appearance is mostly orange or blue, are generally marked with safety certification mark (such as UL, CSA and other logo) and pressure AC250V or AC275V words. However, its true DC withstand voltage is above 5000V. It must be emphasized that the Y capacitor can not be used with a nominal capacitor such as the nominal voltage AC250V or DC400V.
They all belong to the safety capacitor, which requires the capacitance value can not be too large, and the pressure must be higher. Under normal circumstances, work in the subtropical machine, the required leakage current can not exceed 0.7mA; work in the temperate machine, the required leakage current can not exceed 0.35mA. Therefore, the total capacity of the Y capacitor is generally not more than 4700PF (472).
At the AC power input, it is generally necessary to add three safety capacitors to suppress EMI conduction interference. AC power input is divided into three terminals: FireWire (L) / Neutral (N) / Ground (G). Between the line of fire and the ground and between the zero line and ground in parallel with the capacitor, generally referred to as Y capacitor. The two Y-capacitor connection position is more critical, must meet the relevant safety standards, to prevent electronic equipment leakage or chassis charged, easy to endanger personal safety and life.
