Led interference suppression capacitor: correct sizing and connection

LED interference suppression capacitor: properly dimensioned and connected

With an interference suppression capacitor you can solve some common LED problems. These include flashing or glowing lamps. Here you will learn how to choose a suitable capacitor and how it must be connected in your electrical installation.

What is a suppressor capacitor for LEDs?

A LED interference suppression capacitor is an electrical component for the elimination of leakage currents. These can occur in some electrical installations and cause annoying effects such as LED lighting glowing or flashing. The interference suppression capacitor ensures that unwanted leakage currents are dissipated and is therefore often referred to as the Leakage capacitor designates.

These terms are most commonly used for an LED capacitor and basically mean the same thing:

  • Interference suppression capacitor
  • Leakage capacitor
  • Interference suppression filter
  • Mains filter

However, only the first two designations are correct. The terms Suppression filter and Mains filter are to be understood in the context only colloquially, because a filter circuit is normally more complex and serves the removal of high-frequency disturbances.

If your LED lamp does not have a protective earth, a X2-Capacitor the right choice.
Miflex X2 KSPpz-5 at Amazon

For LED lamps with protective earth a X1Y2 or X2Y2-Capacitor the right choice.
Miflex X1Y2 KSPpz-10-2 at Amazon

How does an interference suppression capacitor work??

In general, a capacitor has a capacity and can be used as an energy storage or as a reactance or a reactance resistor. act as a frequency-dependent resistor. In the 50Hz AC mains, a low capacitance capacitor connected in parallel has a high reactance in the KOhm range.

When the lamp is switched on, the capacitor is virtually not noticeable. When switched off, however, any leakage current present is dissipated via the reactance of the capacitor.

You can find more details about the function of interference suppression capacitors at Conrad Elektronik.

Advantages of a LED capacitor

The use of interference suppression capacitors to solve annoying LED problems has many advantages. These include:

  • Favorable price
  • Simple retrofitting
  • Different designs

Special features of an interference suppression capacitor

A special interference suppression capacitor does not differ in its actual function from a normal capacitor. The special features of an interference suppression capacitor are mainly its robustness against voltage peaks and reliable isolation. These points are extremely important especially when used on 230V mains voltage.

Use only approved interference suppression capacitors to solve the LED problems.

LED capacitor with approval

When does a capacitor in the LED lamp help??

An interference suppression capacitor for LEDs provides a remedy for problems in connection with the electrical installation. A distinction must be made between these basic types of mains interference:

  • Disturbance from the mains
  • Interference in the mains

Interference from the power grid can cause problems with LED lighting. If the LED itself causes disturbances, these can be fed back into the power supply system and influence other consumers.

LED lamps flash

In some cases the LED lamps flash when switched off or flash regularly. Common causes are inductive or capacitive couplings. The switching power supply in the lamp is activated by the resulting leakage current and switches on the LED. The voltage collapses, causing the LED to go out again. This process is now repeated continuously, causing the annoying flashing noise.

The capacitor is connected in parallel with the LED lamp, which diverts the leakage current. The power supply unit of the lamp is no longer activated, so there is no flashing anymore.

LEDs glow after

In some electrical installations, the connection of the LED lamp is not completely voltage-free even after switching it off. Cause are also here capacitive or inductive effects. A small residual voltage is sufficient for the LED illumination to remain permanently lit.

If an interference suppression capacitor is connected in parallel to the lamp, the residual voltage collapses and the LED goes out.

Crackling in the radio or television

Some LED lamps and light sources cause loud crackling noises in the loudspeaker of a running radio or TV when switched on or off. In this case, the fault is caused by the LED lamp and spreads through the mains to the other connected devices.

The cause is usually a poorly suppressed power supply in the LED lamp. This problem often occurs with cheap noname lamps, because here the electronics were saved. The use of an interference suppression capacitor can prevent the annoying crackling noise.

Selection and dimensioning of the LED capacitor

Suppression capacitors are divided into different classes and should be selected depending on the application. To fix most LED problems, these classes are especially suitable:

  • X2-Capacitor
  • Y2-Capacitor
  • X1Y2-capacitor
  • X2Y2-Capacitor

X2 interference suppression capacitor

A frequently used type is the X2-capacitor. This helps to divert leakage currents on the phase (L) against the neutral conductor (N).

X2 Suppression capacitor Miflex KSPpz-5

Y2 interference suppression capacitor

The Y2-capacitor is used to divert leakage currents from phase (L) and neutral (N) to the protective conductor (PE). So here you would need two capacitors. Ideally, these should still be connected to the aforementioned X2-capacitor can be combined. However, the use of one of the following combination capacitors is usually more sensible than installing three individual capacitors.

X1Y2 Suppression Capacitor

A X1Y2-capacitor is a mixture of the previously mentioned types. The capacitance of the X2 capacitor is between phase and neutral conductor. Capacitances of Y2 capacitors are between phase and protective conductor and between neutral and protective conductor.

X1Y2 LED capacitor Miflex KSPpz-10-2

X2Y2 Suppression capacitor

A X2Y2-capacitor is electrically identical to the previously mentioned X1Y2 type. The difference between X1 and X2 lies in the classification. X1 capacitors are designed for even higher peak voltages. The X2 version is just as sufficient for operation on 230V mains.

Rated voltage

When choosing you should pay attention to the class (X1/X2/Y2) and a sufficient dielectric strength. The mains voltage in Germany is 230V and has a maximum tolerance of 10%. The interference suppression capacitor should be at least a 250V type, better a 275V or 300V type.


The capacitance of a X1 or X2-capacitor should be between 0.1uF and 0.4uF. The capacitance of the Y2-capacitor should be between 2.2nF and 2.7nF. As can be seen in the figure above, the Y2-capacitance is also given in uF by some manufacturers. 0.0027uF corresponds exactly to 2.7nF.

When to use which type?

At first glance, the selection of interference suppression capacitors seems rather confusing. On closer inspection, however, you only need to distinguish between two cases.

If your LED lamp has no protective conductor, a X2-Capacitor the right choice.
Miflex X2 KSPpz-5 at Amazon

For LED lamps with protective earth a X1Y2 or X2Y2-Capacitor the right choice.
Miflex X1Y2 KSPpz-10-2 at Amazon

Connect the interference suppression capacitor correctly

As described before, for interference suppression of the LED illumination, on the one hand X2-Capacitors, Y2-capacitors or their mixed form are used. With the mixed variants all capacitors are in one housing resp. component.

The X2-capacitor is connected between phase (L) and neutral (N).

The black connection cables are connected to the phase (L) and the neutral conductor (N). The wire with the transparent insulation is connected to the protective conductor (PE).

It is recommended to install the interference suppression capacitor as close as possible to the LED luminaire. If there is enough space, the capacitor can be connected to the luster terminal of the luminaire. Alternatively, the capacitor can be placed in the junction box to the lamp.


The problems mentioned in the electrical installation can usually be solved quite easily with an interference suppression capacitor. You now know the different LED capacitors and what to look for when choosing and how to install them.

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