Class-X and Class-Y capacitors are safety-certified and generally designed and used in AC line filtering in many electronic device applications. These safety capacitors are also known by other names, including EMI/RFI suppression capacitors and AC line filter safety capacitors. (EMI stands for electromagnetic interference. Class-X and Class-Y capacitors are classified according to: 1. their peak voltage/rated voltage and 2. the peak impulse voltage that they can safely withstand. Tables 1 and 2. Subclass X2 and Y2 are the most commonly used safety-certified capacitors. Depending upon your own application and requirements, they are probably the ones you'll want to use. This is assumed because X2 and Y2 safety. Because Class-X and Class-Y capacitors must be connected directly to AC lines (line-to-neutral or line-to-ground) in order for them to perform their EMI and RFI filtering functions, they. All safety-certified capacitors should have the proper logo markings/symbols on their casing. See Figure 4 below for an example and see Figure 5.
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What is a safety capacitor?
One of these techniques is the use of so-called safety capacitors, also known as Class X and Class Y capacitors. These capacitors are not special or unique. Just like a decoupling capacitor, the term “safety” refers to the function and placement of the capacitor, not to a specific type of capacitor.
These safety capacitors are also known by other names, including EMI/RFI suppression capacitors and AC line filter safety capacitors. (EMI stands for electromagnetic interference and RFI stands for radio-frequency interference; RFI is simply higher-frequency EMI.) Figure 1. An example of a Class-Y capacitor. Image from this teardown.
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.
Where are safety capacitors located in a power supply?
In isolated power supplies, safety capacitors are placed primarily in two locations: In the first case, Class X and Class y capacitors are placed in EMI filter circuits on the front end of a power supply.
What are the different types of Safety capacitors?
Two common types that can fit the role of safety capacitors are multilayer ceramic capacitors (MLCCs) and plastic film capacitors. Each has its benefits depending on the specific application. Some characteristics to consider when choosing between capacitors include the following:
How do I choose a Class X & Y safety capacitor?
To be clear, you should select your Class-X and Class-Y capacitors according to your design's purpose and requirements. Whereas X2 and Y2 caps are appropriate for household applications, X1 and Y1 safety capacitors are used in industrial settings.