Safety capacitor are used to suppress electromagnetic interference and filter, playing a protective role in electronic products. This article provides a detailed explanation of the functions, differences, and applications of safety capacitors in electronic products.
Safety capacitor are divided into X capacitors and Y capacitors.
Understanding X capacitor
The full name of the X-capacitor is generally:: X2 (X1/X3/MKP), a capacitor used to suppress electromagnetic interference in power supplies. Generally, its main functions in the circuit are: power cross-line circuit, EMI filtering, spark elimination circuit, etc. to ensure that the finished electronic products meet EMC requirements.So safety capacitors are often seen in electronic products.
X capacitor is between the live and neutral wires. The x capacitor is used in power supply filtering to filter the power supply and filter differential mode interference.
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 to both ends of the X capacitor to prevent the power cord plug from being charged for a long time due to the charge and discharge process of the capacitor when the power cord is unplugged and plugged in. Safety standards stipulate that when the power cord of a working machine is unplugged, within two seconds, the live voltage (or ground potential) at both ends of the power cord plug must be less than 30% of the original rated working voltage.
X capacitors are often referred to as "line-to-line" or "across-line" Safety capacitors and are used to reduce EMI/RFI caused by the differential mode noise of the AC power supply.The X capacitor is connected across the live and neutral wires to filter out negative effects caused by conducted interference, voltage surges and voltage transients. The X capacitor provides a clean AC signal to the circuit and is therefore affected by all AC line changes, which can be dangerous if the capacitor's voltage or power threshold is exceeded. Due to the special design of the X capacitor, its failure mode is short circuit, which triggers the circuit breaker or the fuse to open under overstress. If overcurrent protection is not installed or unresponsive, X capacitors pose a huge risk of fire.
X capacitor are usually metallized film, the capacitance capacity is μF level, most of them are square, the surface is marked with a safety certification mark, and the word voltage withstand is usually AC300V or AC275V.
Understanding Y capacitor
Y capacitors, often called "line-to-ground" or "bypass"Safety capacitors, are placed across the live and ground wires to handle EMI/RF caused by common-mode noise. Y capacitors can also be affected by AC line changes due to conducted interference, overvoltage surges and voltage transients, which can cause capacitor failure and cause danger if the capacitance threshold is exceeded. The special design of the Y capacitor is different from that of the X capacitor. Its failure mode is an open circuit, causing the circuit to be affected by unfiltered AC power. The risk of fire caused by Y capacitors is low.
Y capacitor are usually ceramic capacitors, appearing in pairs, most of which are flat round and blue in appearance, and their capacitance is nF level, based on leakage current constraints, Y capacitance cannot be very large.
X capacitor vs Y capacitor: Key Differences
| X capacitor | Y capacitor | |
| Function | Filtering of differential mode interference | Common mode interference filtering |
| Application | DC circuit or low frequency circuit | AC Circuit |
| Connect | Between the fire (L) and zero (N) wires | Between the firewire to earth (L and earth) and the zero wire to earth (N and earth) Usually appear in even numbers |
| Color | Yellow | Blue |
| Capacity Unit | Microfarad (μF) | Nanofarad (nF) |
| Materials | Metallized film | Ceramic |
X Capacitor are a capacitor connected between the two lines of the power line (L-N), and generally a metal film capacitor is used;
Y Capacitor are connected between the live wire and the ground (L and the earth) and between the neutral wire and the ground (N and the earth), and usually appear in pairs.. Based on the limitation of leakage current, the Y capacitor value cannot be too large.
Generally, the X capacitor is uF level and the Y capacitor is nF level. The X capacitor suppresses differential mode interference, and the Y capacitor suppresses common mode interference.
Guidelines for the use of safety capacitors
1. Safety capacitors used to suppress electromagnetic interference from power supplies
When using capacitors in power jumper circuits to eliminate noise, not just normal voltages, but also the generation of abnormal pulse voltages (such as lightning) must be taken into account, which may cause the capacitors to smoke or catch fire. Therefore, the safety standards of cross-line capacitors have strict regulations in different countries, so capacitors that have passed safety certification must be used.
2. It is not allowed to use DC capacitors as cross-line safety capacitors:
X2 type capacitors used to suppress electromagnetic interference in power supplies should be used in situations where the failure of the capacitor will not cause an electric shock hazard. For example, the power supply is connected across lines and can withstand a pulse voltage of 2.5kV.
Y2 type capacitors used to suppress electromagnetic interference in power supplies should be used in situations where the failure of the capacitor will not cause the risk of electric shock. When used to connect the power supply across lines, they can withstand a pulse voltage impact of 5kV without causing breakdown.
X capacitor (line to line)
Y capacitor (line to ground)
Classification and characteristics of safety X capacitors and Y capacitors
Properties: X capacitors and Y capacitors are mostly used in switching power supplies, and they are both safety capacitors. Safety capacitors are used in situations where failure of the capacitor will not cause electric shock or endanger personal safety.
X Capacitor Features
Appearance capacitance: mostly yellow, square, uF level capacitors.
Function: X capacitor is mainly used to suppress differential mode interference.
Location: Connected between live and neutral wires.
Category: X1/X2/X3
X1: Withstand high voltage greater than 2.5 kV, less than or equal to 4 kV
X2: Withstand high voltage less than or equal to 2.5 kV,
X3: Withstand high voltage less than or equal to 1.2 kV
PS: 1. There are relatively few X3 safety capacitors in various industries, and X2 standards are generally used.
Y Capacitor Features
Appearance capacitance: mostly blue, oblate, and nF level capacitors. Due to the consideration of leakage current, the Y capacitance is generally not greater than 4700pF.
Function: Y capacitor is mainly used to suppress common mode interference.
Location: Connected to live wire and ground; Between the zero line and the ground.
Classification: Y1/Y2/Y3/Y4
Y1: Rated voltage ≤ 500VAC, peak voltage ≤ 8 kV, experimental voltage 4000VAC.
Y2: The rated voltage is 150VAC-500VAC, the peak voltage is equal to 5 kV, and the experimental voltage is 1500VAC.
Y3: High voltage resistance n/a, has been replaced.
Y4: The rated voltage is less than 150VAC, the peak voltage is equal to 2.5 kV, and the experimental voltage is unknown.
Types of X and Y Safety capacitors
X and Y safety capacitors filter AC signals and reduce EMI, so they are directly connected to hazardous AC mains voltages and must be certified as "safety capacitors" to ensure safe operation under these conditions. There are various types of safety capacitors used in safety filter circuits. Although the applications are not limited to this, ceramic surface mount and ceramic disk safety capacitors are often used in interference suppression and AC line filtering applications, while film capacitors are usually used to attenuate conducted emissions.
Ceramic capacitors or film capacitors can be used as X or Y capacitors, but factors such as the shape and characteristics of the capacitor will make a certain type of capacitor more suitable for certain applications. Ceramic capacitors are commonly used in antenna coupling, primary and secondary coupling such as switching power supplies, and line interference suppression such as high-speed switching control of motor controls, relays, switching power supplies, and inverters. Film capacitors have self-healing properties, making them ideal for capacitive power supplies, electric meters, automotive applications, and harsh environmental conditions.
In conclusion
X and Y safety capacitors filter AC power lines to reduce EMI and RFI in sensitive electronic applications. X and Y capacitors are each classified with the ability to withstand different levels of continuous AC, peak pulse voltages and voltage transients. Safety capacitors are essential regardless of the application to power signal-sensitive electronic equipment while reducing the risk of fire or electric shock.
