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How safety capacitors work? - Case

How safety capacitors work?

447 Published by at October 14,2019

How safety capacitors work


Safety capacitors refer to safety capacitors that do not cause electric shock after the capacitor fails, and do not endanger personal safety. Safety capacitors are typically only used for filtering in anti-jamming circuits. They are used in the power supply filter to filter the power supply and filter the common mode and differential mode interference respectively.

For safety reasons and EMC considerations, it is recommended to add a safety capacitor at the power inlet.

The discharge of the safety capacitor is different from the ordinary capacitor. The charge will remain for a long time after the external power supply is disconnected. If it is touched by hand, it will be charged, and the safety capacitor has no such problem. At the AC power input, it is generally necessary to add three safety capacitors to suppress EMI conduction interference.

Safety capacitors are used in applications where the capacitor does not cause an electric shock and does not endanger personal safety.

It includes two types of X capacitors and Y capacitors. The x capacitor is a capacitor that is connected between the two lines of the power line (LN). Generally, a metal film capacitor is used. The Y capacitor is connected between the two lines of the power line and the ground (LE). , NE) capacitors are generally present in pairs. Based on the limitation of leakage current, the value of Y capacitor should not be too large. Generally, the X capacitor is uF grade, and the Y capacitor is nF grade. The X capacitor suppresses differential mode interference and the Y capacitor suppresses common mode interference.

Safety Capacitor Working Principle: When the pressure directly acts on the surface of the measuring diaphragm to make a slight deformation of the diaphragm, the high-precision circuit on the measuring diaphragm transforms this tiny deformation into a highly linear, proportional to the pressure. The voltage is also proportional to the voltage signal.
The discharge of the safety capacitor is different from the ordinary capacitor. The charge will remain for a long time after the external power supply is disconnected. If it is touched by hand, it will be charged, and the safety capacitor has no such problem. For safety reasons and EMC considerations, it is recommended to add a safety capacitor at the power inlet. At the AC power input, it is generally necessary to add three safety capacitors to suppress EMI conduction interference. They are used in the power supply filter to filter the power supply and filter the common mode and differential mode interference respectively.

Peak pulse voltage overvoltage level allowed in safety capacitor safety class applications (IEC664)
X1 》2.5kV ≤4.0kV III
X2 ≤2.5kV II
X3 ≤1.2kV ——
Safety Capacitor Safety Level Insulation Type Rated Voltage Range
Y1 double insulation or reinforced insulation ≥ 250V
Y2 basic insulation or additional insulation ≥150V ≤250V
Y3 basic insulation or additional insulation ≥150V ≤250V
Y4 basic insulation or additional insulation "150V

The capacitance of the Y capacitor must be limited to control the amount of leakage current flowing through it at rated frequency and rated voltage and the effect on the EMC performance of the system. G***151 specifies that the capacity of the Y capacitor should be no more than 0.1uF. In addition to the corresponding grid voltage withstand voltage, the Y capacitor also requires sufficient safety margin for electrical and mechanical performance to avoid breakdown and short circuit under extreme environmental conditions. The pressure resistance of the Y capacitor is correct. Protecting personal safety is of great significance.

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