1. Safety capacitor
Definition of safety capacitors: Safety capacitors are used in situations where failure of the capacitor will not cause electric shock or endanger personal safety. It includes X capacitor and Y capacitor.
2. Definition of X and Y capacitors
X capacitor: The X capacitor is a capacitor connected between the two lines (LN) of the power line. It is usually used to filter out differential mode signals.
Y capacitor: Y capacitor is a capacitor connected between the two lines of the power line and the ground (LE, NE). It is generally used to filter out common mode signals.
The main difference between these two capacitors is their connection method and application scenarios.
3. Model classification and parameters
X capacitors are divided into X1, X2, and X3. The main differences are:
- X1 high voltage resistance: 2.5KV＜X1≤4KV;
- X2 high voltage resistance: X2≤2.5KV;
- X3 high voltage resistance: X3≤1.2KV;
Safety capacitor safety level | Peak pulse voltage (withstand voltage) allowed in the application | Overvoltage level (IEC664) | Application occasions | Peak voltage applied in withstand voltage test |
X1 | 2.5KV＜X1≤4KV | III | high peak pulse voltage | C≤1.0uF，4KV； C＞1.0uF，4/√C； |
X2 | X2≤2.5KV | II | Ordinary | C≤1.0uF，2.5KV； C＞1.0uF，2.5/√C； |
X3 | X3≤1.2KV | - | Ordinary |
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Y capacitors are divided into Y1, Y2, Y3, and Y4. The main difference is: (DC voltage resistance level)
- Y1 can withstand high voltages greater than 8 kV;
- Y2 can withstand high voltages greater than 5 kV;
- Y3 withstands high pressure N/A;
- Y4 can withstand high voltages greater than 2.5 kV.
Safety capacitor safety level | Insulation type | electric power | Withstand voltage test (peak) | Withstand voltage test (effective value) |
Y1 | D or R (double insulation or reinforced insulation) | .500V | 8.0KV | 4.0KV |
Y2 | S or B (basic insulation or supplementary insulation) | ≥150V .250V | 5.0KV | 1.5KV |
Y3 | S or B (basic insulation or supplementary insulation) | ≥150V .250V | — | — |
Y4 | S or B (basic insulation or supplementary insulation) | ＜150V | 2.5KV | 0.9KV |
4. Select elements
When selecting X and Y capacitors, you need to consider the following factors:
1. X and Y capacitors must meet the voltage requirements. For those that exceed the nominal voltage, you can choose to use them in series to equalize the voltage, but you must use exactly the same capacitors in series.
2、X，Y电容必须满足温度要求。X电容的额定温度一般在本体会有标示。Y电容的工作温度目前主要有两种，一种是-40℃~+85℃，还有一种是-40℃~+125℃。主要有一种比较老的认证，报备的温度是-40℃~+85℃，现在新的安规认证的要求是-40℃~+125℃。
3. Consider the possible pulse voltage at the input end of the circuit. Different capacitors can withstand different pulse voltages. The withstand voltage of the capacitor cannot be less than the peak value of the pulse voltage in the circuit.
4. As safety capacitors, X and Y capacitors must be certified by a safety testing agency. The appearance of the capacitor is generally marked with safety certification marks (such as UL, CSA, etc.) and the words AC250V or AC275V withstand voltage. It must be emphasized that the X and Y capacitors cannot be replaced by ordinary capacitors with nominal withstand voltage of AC250V or DC400V.
