Understanding RF Chokes: Inductor Types, Applications, and Selection Based on Frequency Range

vermes 10770 1
  • #1
    Level 8  
    A choke in the field of electronics is an inductor that blocks alternating current of a higher frequency. At the same time it allows passing lower frequency or DC current.

    There are several kinds of chokes, and one of them is RF choke (RFC). It is destined to provide high impedance at higher frequencies, used for example in radio communication. A RF choke attenuates the signal in a conductor when an audio amplifier is in proximity to a HF source (it can be a radio transmitter or a computer monitor). Its core is usually made of iron powder or ferrite (for higher frequencies), but it also may be made of non-magnetic cores (for even higher frequencies) and then its inductance is low. The electrical wire wound in a coil is formed in a complicated pattern called a basket , basket-weave or honeycomb winding. Basket winding is designed typically for higher frequencies above 50kHz. One of the most important benefits resulting from application of this type of winding is reduction of the energy losses. Another positive thing about the basket winding is that it reduce self-capacitance and proximity effect losses. However, it causes higher leakage inductance due to the fact that the coil takes relatively a lot of space.

    RF chokes can be used instead of standard inductors which are commonly used for passing or blocking signals. Remember that a RF choke is to pass DC and block (choke) signals of radio frequency. The value of inductance is the parameter that should be considered while deciding on which RF choke to use instead of an inductor. The higher it is, the better RF choke. High value of inductance affects positively the level of attenuation that appears with passing low frequency signals. RF chokes can also be used for wider frequency range than it can be read in their datasheets. The explanation of that phenomenon is that these chokes are equipped with thin wires, so they have too low capacitance to counteract HF resistance of the wire. As a result, their frequency exceeds the frequency range from the datasheet, even above their self-resonant frequency.

    Below there are some tips on how to choose the correct RF choke for your design:

    DC capability should be correct for the bias current you want to use
    The inductance value should be appropriately high
    Size of the package should suit your needs
    Core should be made of material which is capable with the frequency you intend to use.

    Nowadays in modern electronics, there is an interesting example of RF choke called a ferrite bead. That component decreases noises at Radio Frequencies by taking the dissipation of high frequency current in a ferrite ceramic. This RFC helps to avoid interference on both ways: from and to a device. It is a passive electrical component that consists of a cyllindrical core slipped over a wire . A popular application of these ferrite beads is to put them on computer cables, sometimes they form quite large cyllindrical elements put on external cabling of an electrical device, such as USB cables.
  • #2
    Level 25  
    You appear to be master of copy & paste...