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Mains filters | Buy radio interference filters

EMC filters are also known as mains filters and radio interference suppression filters. In short, the electromagnetic compatibility filteris an electronic component or circuit. The circuit is used to suppress electromagnetic interference (EMI) and thus improve the electromagnetic compatibility (EMC) of devices. These mains filters ensure that electrical and electronic devices are less susceptible to interference from the environment. EMC filters also ensure that electrical devices themselves generate less interference that could affect other devices.

History of the EMC filter

The development of EMC filters began in the early days of electronics and electrical engineering when the need to minimize electromagnetic interference (EMI) was recognized. As electrical and electronic devices became more widespread in the 20th century, the amount of unwanted electromagnetic emissions generated by these devices also increased.

EMC filters in the 1960s and 70s

In the 1960s and 1970s, the first systematic approaches to suppressing such interference were developed. This led to the integration of filter circuits into electrical devices to improve electromagnetic compatibility (EMC).

The first EMC filters

The first EMC filters were based on simple combinations of inductances and capacitances. As technology progressed and EMC requirements increased, more complex and efficient filter designs emerged. International standards and regulations, such as the European Union's EMC Directive, also contributed to further development by setting strict limits for electromagnetic emissions and immunity.

EMC filters today

Today, EMC filters are an essential part of modern electronics, ensuring the reliability and safety of devices in an increasingly connected and electrified world.

An EMC filter works as an interference suppression filter by attenuating or blocking unwanted high-frequency interference signals, while the desired low-frequency signals can pass through unhindered. This is achieved by combining passive electronic components.

1. Inductors (coils):

   These components act like resistors for high-frequency signals. If a high-frequency interference hits an inductor, the interference is attenuated and cannot be passed on.

2. Capacitors (capacitors):

   Capacitors divert high-frequency signals to earth or block them by acting as a short circuit for these frequencies. This prevents the interference from penetrating the device to be protected or being emitted by it.

3. Resistors:

   Resistors are also used in some EMC filters to attenuate certain frequencies and improve the filtering effect.

Typically, the EMC filter consists of a combination of these components arranged in different configurations to suppress both common mode interference (same phase on all lines) and differential mode interference (different phases on different lines).

There are different types of EMC filters that are used depending on the application and the type of interference to be suppressed. Here are the most important types of EMC filters:

1. Mains filter (mains EMI filter)

   Used to suppress interference transmitted via the power grid. Often found in household appliances, industrial equipment and consumer electronics.

2. Common mode filters (common mode chokes)

   Suppress common mode interference that occurs in phase on all lines. Used in power supply units, data lines and communication systems.

3. Differential mode chokes (differential mode filters)

   Suppress differential interference that occurs between two lines. Often used in audio and video equipment and in communication systems.

4. Capacitive filters (capacitor filters)

   Use capacitors to block high-frequency interference and allow low-frequency signals to pass. Suitable for use in electronic circuits and power supplies.

5. Inductive filters (coil filters)

   Use inductors to attenuate high-frequency interference. Are often used in combination with capacitors to form LC filters.

6. LC filters (inductor-capacitor filters)

   Combination of inductors and capacitors for effective attenuation of interference. Often found in power supply units, switching power supplies and frequency converters.

7. RC filter (resistor-capacitor filter)

   Combination of resistors and capacitors to suppress high-frequency interference. Often used in electronic circuits and audio applications.

8. PI filter

   Consist of two capacitors and an inductor arranged like the letter "π". Effective in attenuating high-frequency interference in power supply systems.

9. EMC filter (electromagnetic compatibility filter)

   Specially developed to improve the electromagnetic compatibility of devices. Used in communication systems, automotive applications and industrial control systems.

10. Ferrite filters (ferrite cores and ferrite beads)

    Use ferrite materials to suppress high-frequency interference on lines. Commonly found in data lines, USB cables and network cables.

These types of filters are essential for a wide range of applications, from household appliances and industrial equipment to sensitive communication systems, to ensure electromagnetic compatibility and interference-free operation.

There are different types of EMC filters that can be used depending on the application and type of interference. Some of the most common types of EMC filters are:

1. differential mode filters: these filters are typically used to suppress interference that occurs in differential mode, i.e. between the phases or conductors of a circuit. They can be installed both on the mains side and on the load side.

2. common mode filters: These filters are used to suppress interference that occurs in common mode, i.e. on all conductors of a circuit simultaneously. They are often installed on the mains side.

3. LCL filters: These filters consist of a combination of inductors (L), capacitors (C) and chokes (L). They are used to suppress both differential mode and common mode and provide a wider bandwidth for noise suppression.

4. LC filters: These filters consist of a combination of inductors (L) and capacitors (C). They are mainly used to suppress the differential mode and offer a limited bandwidth for noise suppression.

The differences between these filters lie mainly in their configuration, the type of interference they can suppress, the bandwidth of interference suppression and the cost. Some filters can suppress both the differential mode and the common mode, while other filters are specialized in only one of these modes. Choosing the right filter depends on the specific requirements of the application and the interference present.

EMC filters differ mainly in their design, their functional principles and their specific applications. Here is a detailed overview of the differences between the various types of EMC filters:

1. Mains filters (mains EMI filters):

   A mains filter consists of inductors, capacitors and sometimes resistors. It filters high-frequency interference that comes from or is emitted into the power grid. Mains filters are used in household appliances, industrial systems and consumer electronics to ensure electromagnetic compatibility and interference-free operation.

2. Common mode filters (common mode chokes):

   A common mode filter consists of inductors that influence both lines of a pair simultaneously. It suppresses common mode interference on all lines. Common mode filters are used in power supply units, data lines and communication systems to ensure electromagnetic compatibility and interference-free operation.

3. Differential filters (differential mode chokes):

   A differential filter consists of inductors that operate between two lines. It suppresses differential interference that occurs between the lines. These filters are used in audio and video equipment and communication systems to improve signal quality and electromagnetic compatibility.

4. Capacitive filters (capacitor filters):

   A capacitive filter consists of capacitors. It blocks high-frequency interference and allows low-frequency signals to pass through. Capacitive filters are used in electronic circuits and power supply units to improve electromagnetic compatibility and ensure that the devices function without interference.

5. Inductive filters (coil filters):

   An inductive filter (coil filter) consists of inductors that attenuate high-frequency interference. It is often used in combination with capacitors to form LC filters. Areas of application are electronic circuits and power supply units, where it ensures effective interference suppression.

6. LC filter (inductor-capacitor filter):

   An LC filter consists of inductors and capacitors. It effectively dampens interference caused by resonance between these components. LC filters are used in power supply units, switching power supplies and frequency converters to ensure interference-free operation and better electromagnetic compatibility.

7. RC filter (resistor-capacitor filter):

   An RC filter consists of resistors and capacitors. It attenuates high-frequency interference through resistance and capacitance. RC filters are used in electronic circuits and audio applications to improve signal quality and suppress unwanted frequencies, resulting in more stable and reliable performance.

8. PI filter:

   A PI filter consists of two capacitors and an inductor in a π arrangement. It attenuates high-frequency interference in power supply systems. PI filters are used in power supply systems and DC-DC converters to improve electromagnetic compatibility and ensure a stable power supply.

9. Ferrite filters (ferrite cores and ferrite beads):

   Ferrite filters consist of ferrite materials wrapped around cables or wires. They suppress high-frequency interference through the magnetic material of the ferrite. Ferrite filters are used in data lines, USB cables and network cables to ensure interference-free data transmission and better electromagnetic compatibility.

These differences in design and function make it possible to use EMC filters in a targeted manner depending on the requirements and application in order to ensure electromagnetic compatibility and the interference-free functioning of devices.

A mains filter for thyristor controllers is designed to attenuate the steep current rises caused by phase control and the resulting conducted interference emissions. The non-linear switching of the thyristors generates harmonics and high-frequency transients which, without filtering, would exceed the EMC limit values in accordance with EN 61800-3. The filter acts as a low-pass filter that allows the low-frequency mains voltage to pass, while it provides a high series impedance and a low-impedance path to earth for high-frequency interference currents.

In the technical design, engineers must take into account the saturation resistance of the chokes to the high effective value of the load current and the leakage currents of the Y capacitors. Since a line filter thyristor controller often interacts with inductive loads, precise tuning of the filter impedance is required to avoid resonance peaks in the supply network. The choice of a multi-stage filter design improves the insertion loss in the critical range from 150 kHz to 30 MHz and ensures the functional integrity of neighboring sensors and control components.

The EMC mains filter function is based on targeted impedance mismatching. An LC low-pass network reflects high-frequency interference back to the source or diverts it to earth, while the 50 Hz supply voltage passes through virtually unattenuated.

Technically, push-pull interference is minimized by X capacitors and common-mode interference by current-compensated chokes and Y capacitors. This ensures compliance with relevant standards such as IEC 60939 or EN 55032.

The EMI filter function is inextricably linked to a low-impedance high-frequency ground connection. Without a flat, unpainted contact to the housing, the Y capacitors cannot effectively dissipate common-mode interference, resulting in a massive drop in attenuation properties.

Engineers must avoid parasitic inductances caused by long earthing strands. As the inductive resistance increases with the frequency(X L = 2 ⋅ π ⋅ f ⋅ L), even a short supply line makes the filter transparent to HF interference and therefore ineffective.