What is Feedthrough Capacitor?

Ⅰ. What is Feedthrough Capacitor?

1. Definition

The feedthrough capacitor is a three-terminal capacitor that is used to reduce high frequencies. The feedthrough capacitor, unlike regular three-terminal capacitors, is directly installed on the metal panel, resulting in a lower grounding inductance and a negligible effect on the lead inductance. As a result, the feedthrough capacitor provides good filtering. The better the electromagnetic interference suppression effect, especially for high-frequency electronic equipment, the better.

Feedthrough Capacitor

2. Structure and Selection

One (C type) or two (Pi type) capacitors with inner and outer electrodes and ceramics make up the simpler through-core structure.

The through-core capacitor's medium is ceramic, and the capacity of the ceramic capacitor changes as the ambient temperature changes. The filter cut-off rate will be affected by this change in capacity. Ceramic capacitors' capacity temperature change rate is determined by the ceramic medium itself. As a result, selecting an appropriate ceramic media is critical.

Feedthrough Capacitor structure diagram

3. Classification

Type C

This is a low-self-induction device that shields the ground from high-frequency noise interference. It is low-cost and ideal for high-impedance sources and high-load applications.

Type L

This is a capacitor having both inductive and capacitive components that runs through the core. This capacitor is commonly employed in circuits with low impedance sources and high impedance loads, as well as the other way around. It's important to keep in mind that the inductive component should face the low-impedance source.

Type Pi

The Pi type has a low impedance to both the impedance source and the load because it is made up of two capacitive elements and an inductive element sandwiched between them. The Pi type filter outperforms the C and L type structures in terms of high-frequency filtering.

4. Characteristics and Applications

Welded feedthrough capacitors

The most suited product for a small installation space is welded feedthrough capacitors.

Filtering signals, data lines, and AC power lines are the most common applications.

Components for composite circuit filters, telecommunications equipment, transmission equipment, microwave filters, industrial computers;

Smaller size allows for more efficient use of space;

Up to 1000VDC rated voltage;

Various circuit structures are available, including C-type, Pi-type, and L-type circuits.

Structure with a high-temperature range: prevents backflow during installation.

MIL-F-15733 QPL and MIL-C-11015 (CK99) certified filters are available for certification.

Resin sealed threaded feedthrough capacitor

Through-hole nuts and washers for resin-sealed bolt-type through-core capacitors are simple to install.

To ensure good environmental protection, the two ends of the solid shell are sealed with resin.

Micro-extrusion mounting or screw mounting is the ideal choice when welding is not suitable, suitable for microwave and other high-frequency applications; among them, micro-extrusion mounting or screw mounting is the ideal choice when welding is not suitable, suitable for microwave and other high-frequency applications;

Up to 2500VDC/240VAC voltage

MIL-F-15733 approved goods are eligible for certification.

C type, L type, and Pi type circuit structures

High current and high voltage resin sealed feedthrough capacitors

High-current filters are utilized primarily in high-current switching power supply and DC charging systems.

High-voltage filters are primarily employed in high-voltage power supplies, and their solid bolt-type structure makes them simple to install.

Features: up to 100Amps of high current

Up to 2500VDC and 240VAC@400HZ voltages are possible.

Glass-sealed high-performance feedthrough capacitors

It uses glass sealing packaging and has outstanding EMI filtering performance; this product is the best alternative for people who still demand high dependability filtering in difficult settings. From 10KHz to greater than 10GHz, it can be used for broadband high-performance EMI filtering. Series of glass sealants Moisture-proof, corrosion-resistant, and resistant to other extreme environments encountered in military applications.

Power supply, signal line, rocket ignition device, aircraft, military communications, medical equipment, multi-stage filtering are all examples of applications.

Optimized design: a wide range of sizes and forms, as well as C, L, and Pi-type circuits for selection, as well as instantaneous suppression of Pi, T, and TT circuits;

Reliability: In accordance with QPL regulations, manufactured to MIL-F-15733 and MIL-F-28861 specifications.

Space application “S” level FED/MIL certification based on MIL-F-28861: MIL-F-15733 and MIL-F-28861 criteria are met.

Features: The insertion loss ranges from 0.01MHz to 10GHz.

1pF-1mu; F; NPO, X7R, Z5U, and other capacitance and temperature characteristics

Temperature range: -55°C to +125°C; -40°C to +85°C

400VDC 240VAC@400Hz is the maximum voltage value.

30 amps maximum current

Ⅱ. Where can Feedthrough Capacitor Use?

Signals, data lines, and AC power lines, telecommunications equipment, microwave filters, industrial computers, and composite circuit filter components are all examples of where feedthrough capacitors and other filters are employed. A feedthrough capacitor on the computer's CPU high-speed data bus, for example, can successfully reduce noise, while a feedthrough capacitor on the transmitter can effectively suppress interference.

Ⅲ. What is Filtering?

We all know that the higher the voltage or current frequency, the easier it is to produce radiation. There are filters in addition to altering the circuit board and installing the requisite magnetic ring. In many circumstances, appropriate filters are added to limit the interference caused by radiation. The high-frequency interference signal can be considerably reduced in this manner. Common interference filters have an effective filtering frequency range of several kHz to tens of MHz, whereas radio frequency interference filters have an effective filtering frequency range of several kHz to above GHz.

Ordinary capacitors cannot effectively filter out high-frequency noise because they are not perfect capacitors. This is because: 1The capacitor lead inductance generates capacitor resonance, which causes high-frequency signals to have a large impedance and weakens the bypass effect; 2The parasitic capacitance between the wires causes the high-frequency signal to be coupled, reducing the filtering effect.

Ⅳ. How does the Feedthrough Capacitor Filter?

The use of feedthrough capacitors as bypass capacitors, on the other hand, can produce excellent high-frequency filtering effects. Feedthrough capacitors have very low parasitic inductance and bypass impedance, and the high frequency between the input and output terminals is removed due to the isolation installation method. Frequency coupling is a term used to describe when two frequencies are coupled together. Feedthrough capacitors can be used to provide a wide range of RF filters for high-frequency applications, which we refer to as "feedthrough filters." Even at a frequency of 10GHz, the tubular feedthrough capacitor will not cause obvious self-resonance due to its coaxially.

The feedthrough capacitor's medium is ceramic, and the capacity of the ceramic capacitor changes as the ambient temperature changes. The filter cut-off rate will be affected by this change incapacity. As a result, selecting an appropriate ceramic dielectric for feedthrough capacitors is critical. Because the feedthrough capacitor's shell is the opposite electrode and is connected to "ground," high-frequency electromagnetic interference signals are short-circuited to "ground" while passing through the center conductor, and electromagnetic interference is eliminated. The feedthrough capacitor is what it sounds like. The noise filtering principle.

Insertion loss

Insertion loss is a measure of the filter's key performance index, which indicates the filter's quality of performance. The feedthrough capacitor, as depicted in the diagram, is closer to the ideal capacitor.

Ⅴ. Several Forms of Feedthrough Filter

RF filters are another name for feedthrough filters. This filter has a similar shape and construction to feedthrough capacitors, but it also has ferrite cores. This filter usually comes in five different forms to satisfy the needs of different situations: Filters of the C-type, LC-type, -type, T-type, and double T-type types

1. Type C Filter

Type C filters, which are made up of three-terminal or feedthrough capacitors, are designed to reduce high-frequency sounds. It's a low-self-induction device that shields the ground from high-frequency noise. It is low-cost and ideal for high-impedance sources and high-load applications.

2. Type LC Filter

A feed-through filter made up of inductive and capacitive elements is known as an LC-type filter. This filter is commonly employed in circuits with low-impedance sources and high-impedance loads, as well as the other way around. It's important to keep in mind that the inductive component should face the low-impedance source.

3. Type π Filter

It is made up of two capacitive elements and an inductance element sandwiched between them, and it has a low impedance to both the impedance source and the load. The -type filter outperforms the C-type and LC-type structures in terms of high-frequency filtering.

4. Type T filter

Two inductance elements and one capacitance element make up a T-type filter. Its circuit topology reveals that both ends' inputs have high impedance. It has a structure that is similar to that of the -type filter, although it is not generally employed in the -type filter and can be used in switching conversion.

5. Type double T Filter

The double T filter is made up of two high-performance T-type filters with more stringent circuit requirements.

The simple through-core structure consists of one (C type) or two (type) capacitors made up of inner and outer electrodes and ceramics. This type of capacitor has a capacity of up to 10pF and a working voltage of up to 2000VDC. The plug-in C-type feedthrough filter is shown in the following diagram, however, soldered feedthrough filters are especially crucial for electrical equipment with limited installation space.

Ⅵ. Installation Precautions

Due to the unique structure of the feedthrough capacitor and feedthrough filter, the housing of the filter must be suitably connected to the panel's ground in order to provide an effective path for interference to pass through. therefore:

1) A disc-shaped multilayer or tubular ceramic capacitor serves as the through-core filter's core. Sudden temperature changes, mechanical vibration, and excessive voltage will all harm them, just like other ceramic things. When placing the through-core filter on the board, take care when welding the filter's guide pin and shaping it to avoid any tension.

2)When installing threaded through-type filters to a partition or panel, the suggested installation rotation force relative to the housing should be applied. Otherwise, the distortion of the shell may cause harm to the inside capacitor.