How to identify X capacitor and Y capacitor? What's the role of X capacitor and Y capacitor?
source:KF Quality author:KFQ 2021-01-23 20:59:54
During internal check against CDF
for an electric appliance inspection, we always noticed critical components X
capacitor and Y capacitor. Then how to identify them and what's the role of
them in a circuit?
In principle, Electro-Magnetic
Interference mainly comes from two aspects, namely conducted interference and
radiated interference.
-Conducted interference
Due to the existence of
parasitic parameters in the circuit and the turn-on and turn-off of the FM
switching device in the switching power supply, the switching power supply
produces large common mode interference and differential mode interference at
the AC input of the mains.
-Radiation interference
Since the change of the
current in the conductor will produce a changing magnetic field in its
surrounding space, and the changing magnetic field will produce a changing
electric field. The amplitude and frequency of this changing current determine
the magnitude and range of the electromagnetic generated by it.
EMI design is a very important part of the circuit, and X capacitors and Y capacitors are important components. General regular power supplies have one EMI and two EMI. The EMI circuit of the power supply uses some of the characteristics of inductive and capacitive components to filter out harmful electromagnetic interference in power or electronic engineering. To put it simply, it acts as a filter for impurities, just like a filter. With the two-stage EMI filter circuit, it is possible to filter out high-frequency clutter and in-phase interference current from the power grid, and at the same time weaken the electromagnetic radiation generated in the power supply to a very low limit, so that the leakage electromagnetic radiation Will not affect the human body or other equipment.
The X capacitor is the
capacitor connected between the live line and the neutral line (L-N). The X
capacitor can suppress differential mode interference and play a role in power
supply filtering. Metallized film capacitors are usually used, and the
capacitance is uF. X capacitors are mostly square, which is similar to the
shape of a box. On its surface, it is generally marked with safety
certification marks, withstand voltage (usually AC300V or AC275V), relying on
standards and other information. Although X capacitor is a kind of CBB
capacitor, not every CBB capacitor can be used as X capacitor, and it must meet
safety standards. X-type safety capacitors are divided into three types
according to withstand voltage: X1, X2, and X3. The allowable peak pulse
voltage and overvoltage levels in the safety class of safety capacitors: 2.5kV＜X1≤4.0kV, 1.2kV<X2≤2.5kV, X3≤1.2kV.
Y capacitors are connected
across the power line and the ground (L-E, N-E) capacitors, generally appear in
pairs to eliminate common mode interference. It is mainly to provide the
fastest loop channel for high-frequency signals and reduce the impact of
high-frequency signals on the system. They are usually ceramic capacitors,
which usually appear in groups. Most of them have an oblate appearance and the
color is blue, which can suppress common mode interference. The Y capacitor
capacity is nF.
Attached picture is the illustration
of circuit drawing, it showed how X capacitor and Y capacitor are connected.
From kfquality.com