The role of safety capacitor
The role of safety capacitor
Electronic Engineering Album
The safety capacitor is divided into X capacitor and Y capacitor
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 location is more critical, must meet the relevant safety standards,
To prevent electronic equipment leakage or chassis charged, easy to endanger personal safety and life. 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).
In particular, as a safety capacitor Y capacitor, requires the need to obtain safety testing agency certification.
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.
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. 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.
As an X capacitor of one of the safety capacitors, it is also required to obtain the certification of the safety inspection mechanism. X capacitors are generally marked with safety certification mark and pressure AC250V or AC275V words, but the real DC voltage up to 2000V or more, when used not to use the nominal voltage AC250V or DC400V like the ordinary capacitor to replace.
Usually, X capacitor multi-choice ripple current relatively large polyester film capacitors. This type of capacitor, larger, but it allows instantaneous charge and discharge current is also large, and its internal resistance is relatively small.
Common capacitance ripple current indicators are very low, dynamic resistance is high. With ordinary capacitors instead of X capacitors, in addition to capacitive voltage can not meet the standard, the ripple current index is also difficult to meet the requirements.
X Capacitance: mainly used in L and N before the capacitor.
Y Capacitance: for L and G or between N and G.
The above two types of capacitors used in the case of equipment, must have certification before.
According to IEC 60384-14
X capacitance is divided into three categories:
Use the peak pulse voltage when using the application range
X1> 2,5KV and <= 4,0KV high pulse when used
X2 <= 2,5KV general purpose
X3 <= 1,2KV general purpose
Y capacitor mainly classified four categories
Classification Rated voltage range Durability test before the peak pulse voltage
Y1 <= 250V 8,0KV
Y2> = 150V and <= 250V 5,0KV
Y3> = 150V and <= 250V none
Y4 <150V 2,5KV