Damping bead
A damping bead ( English ferrite bead ), also known as ferrite bead denotes the attenuation is high-frequency interference on lines that carry signals of low frequency or DC voltages such. B. on power supply lines or lines of RS-232 signals (serial interface) . In contrast to the standing wave filters , the signal wires in the case of damping pearls are fed individually through the ferrite core . There are also cores with several holes through which wires are already passed.
Their counterpart in SMD design, which is identical in terms of purpose but has a different structure, is called SMD ferrite .
Ferrite cores through which conductors are passed act like a choke with low inductance. At very high frequencies, the component acts like an inductance with high losses and a large reactance . The losses prevent resonances with parasitic and line capacities . For this reason, inductors with high quality are usually not well suited as interference filters.
Added to this is the high permeability of the ferrite material compared to air and thus a lower number of turns with a comparable inductance . Few or one turn means a lower parasitic capacitance and correspondingly lower coupling capacitance.
Ferrite beads dampen high-frequency interference pulses on signal and supply lines of devices or reduce their leakage from the device or the spread on the connected lines. Steep edges and overshoots of the signal are flattened and reduce the resulting interference. If necessary, the wire legs of electronic components are also provided with them in order to reduce disturbances where they arise. One example is reducing the effects of diode reverse recovery time .
This type of filtering takes place on or in the device in the immediate vicinity of the connector. For this purpose there are connectors with a built-in large piece of ferrite, which is provided with holes for each pin.
Equivalent circuit diagram and circuit symbol
The equivalent circuit diagram of a damping bead illustrates the characteristic curve
Switching symbol of a damping bead
