Feed-through capacitor
Feedthrough capacitors (also briefly Duko called) are coaxially constructed capacitors , the one electrical line by a conductive wall ( shield lead).
One electrode is led out on both sides as a wire at the ends of a sleeve that acts as a dielectric. This is conductively coated or surrounded by a second sleeve, which represents the second electrode. The external electrode is soldered into the housing wall or contacted in some other way. The capacitor acts as a suppressor by means of the capacitance between the connections and the sleeve.
Feed-through capacitors , together with the circuit behind them or with the connecting lines, form a low-pass filter with a central capacitance to ground. High frequencies are blocked, low frequencies and direct current are allowed through. Often the connections have attached ferrite beads to improve the filter effect; Such a T-element consists of two inductors and the centrally located blocking capacitor.
They prevent high-frequency interference emissions and increase immunity to high-frequency interference signals. With their low-inductance mounting, they offer protection against common-mode signals up to very high frequencies. The capacitance value of suitable ceramic capacitors made of a ceramic tube, which is provided with a solderable outer coating and an inner conductor, is relatively low (up to approx. 100 nF). Such feedthrough capacitors are often used in the power supply of high-frequency circuits such as UHF amplifiers and UHF tuners.
There are also ceramic feedthrough capacitors and foil capacitors in a metal housing with a flange ; these are inserted and screwed through the hole in the shielding housing. They are therefore also suitable for non-solderable housings.
literature
- Adolf Schwab: Electromagnetic Compatibility . 3. Edition. Springer, 2013, ISBN 978-3-662-06980-6 , Chapter 4.1.5: Passive interference suppression components, filter designs, p. 182-183 .