In electronics, choke is an inductor used to block high-frequency AC (AC) currents in an electrical circuit, when it passes a low frequency or direct current (DC). Chokes usually consist of insulated wire reels that often hurt magnetic cores, although some consist of donut-shaped "bead" of ferrite material suspended on a wire. The choke impedance increases with frequency. Its low electrical resistance passes through AC and DC with less power loss, but reactance limits the amount of air conditioning that is bypassed.
The name comes from blocking - "choking" - high frequency when passing low frequency. This is a functional name; the name "choke" is used if the inductor is used to block or separate the higher frequencies, but is simply called "inductor" if used in electronic filters or tuned circuits. The inductor designed for use as a choke is usually distinguished by having no low-loss construction (the high Q factor) required in the inductor used in the tuned circuit and filtering application.
Video Choke (electronics)
Type and construction
Chokes are divided into two major classes:
- Audio frequency chokes (AFC) - designed to block audio and power lines while allowing DC to pass Radio frequency chokes (RFC) - designed to block radio frequencies while allowing audio and DC to pass.
Audio frequency chokes
Audio frequency chokes (AFC) usually have a ferromagnetic core to increase their inductance. They are often built similar to transformers, with laminated iron cores and air gaps. The iron core helps to increase the inductance. The main use in the past is in direct rectifiers and motor current controllers to produce direct current (DC), where they are used in conjunction with large electrolytic capacitors to remove the voltage ripple (AC) at the DC output. Rectifier circuits designed for choke-output filters can produce too much DC output voltage and are subject to rectifier and filter capacitors to excessive currents and roots if inductor is removed. However, modern electrolytic capacitors with high ripple current ratings, and voltage regulators that eliminate more power supply ripples than can be choked, have eliminated heavy heavy blockages from mainstream power supplies. Smaller chokes are used in switching power supplies to remove high frequency switching transients from output and sometimes from feed back to parent input. They often have a toroidal ferrite core.
Some DIY car audio enthusiasts use coil chokes with car audio systems (especially in wires for subwoofers, to remove high frequencies from reinforced signals).
Radio frequency chokes
Radio frequency chokes (RFCs) often have iron powders or ferrite cores that increase overall inductance and operation. They are often wound in a complicated pattern (a winding basket) to reduce the capacitance and loss of proximity effects. Chokes for higher frequencies have a non-magnetic core and low inductance.
The modern form of choke that is used to remove digital RF noise from the line is the ferrite bead, cylindrical core or torus of ferrite that slips the wire. This is often seen on computer cables. Common RF choke values ​​can be 2 milihenries.
Common mode (CM) chokes
Common-mode chokes, where two windings are wrapped around a single core, are useful for suppressing electromagnetic interference (EMI) and radio frequency interference (RFI) from the power supply channel and to prevent malfunctions of power electronics devices. It passes the differential current (the same but opposite), while blocking the common mode current. The magnetic flux generated by the differential-mode current (DM) in the core tends to cancel each other since the negative windings are combined. Thus, the choke presents little inductance or impedance to the DM current. Usually this also means that the core will not saturate for large DM currents and the maximum current rating is determined by the heating effect of the winding resistance. CM currents, however, see a high impedance due to the combined inductance of the positive paired windings.
CM Chokes are commonly used in industrial, electrical and telecommunications applications to eliminate or reduce noise and associated electromagnetic interference.
Reduced emission of near magnetic field
When CM choke performs CM currents, most of the magnetic flux generated by the windings is limited to the inductor core due to its high permeability. In this case, the leakage flux, which is also a near field magnetic emission from the low CM choke. However, the DM current flowing through the winding will produce a near high magnetic field because the negative windings are combined in this case. To reduce near field magnetic emissions, the winding winding structure can be applied to CM choke.
The difference between a winding winding balanced CM choke and a conventional balanced two winding CM choke is that the winding interacts in the center of the open core window. When conducting CM currents, a balanced rotary winding inductor CM can provide a CM inductance identical to a conventional CM inductor. When doing a DM current, the equivalent current loop will produce an inverted magnetic field in space so they tend to cancel each other out.
Measurement for near-field magnetic emission
We need to do the current to the inductor and use the probe to measure near field emissions. First, the signal generator, serves as a voltage source, connected to the amplifier. The output of the amplifier is then connected to the inductor below the measurement. To monitor and control the current flowing through the inductor, the current clamp is clamped around the conductor wire. Next, the oscilloscope is connected to the current clamp to measure the current waveform. A probe is then used to measure the flux in the air. Other spectrum analyzers connect to the probe to collect data.
Maps Choke (electronics)
References
Further reading
- Wildi, ThÃÆ'Â © odore (1981) Power technology , ISBNÃ, 978-0471077640
See also
- Reactor line
External links
- Common Choke Theory Theory
Source of the article : Wikipedia
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