What is a choke

 In electronics, a choke is an inductor used to block high-frequency AC current while making direct current (DC) and low-frequency AC current in (AC) circuits. A choke usually consists of a coil often wound around the magnetic core of an insulated wire, although some are made of an annular "bead" of ferrite material on a string of wires. The impedance of choke coil increases with the increase of frequency. Its low resistance passes through AC and DC with almost no power loss, but its reactance limits the throughput of AC.

 Type and structure of choke

 MF or HF radios are used for a tenth ampere choke and a ferrite bead VHF several ampere choke. A ferritic "bead" choke is a cylinder of ferrite that surrounds the power cord of the computer to prevent electronic noise.

 Chokes are divided into two categories:

 Audio choke (AFC) – designed to block audio and power line frequencies while allowing DC to pass through

 Radio frequency choke (RFC) – designed to block radio frequencies while allowing audio and DC to pass through.

 Audio choke

 Audio choke (AFC) usually has a ferromagnetic core to increase its inductance. Their construction is usually similar to that of transformers, with laminated cores and air gaps. For a given core volume, the core increases inductance. Choke is often used in the design of vacuum tube rectifier power supply, radio receiver or amplifier and other equipment. They are commonly used in DC motor controllers to generate direct current (DC) and are used in combination with large electrolytic capacitors to eliminate voltage ripple (AC) at the output DC. The rectifier circuit designed for the choke output filter may generate excessive DC output voltage. If the inductor is removed, the rectifier and filter capacitor will be subject to excessive surge current and ripple current. However, modern electrolytic capacitors with high ripple current ratings and voltage regulators that eliminate more power ripple than chokes have eliminated bulky and bulky chokes in power frequency power supplies. Smaller chokes are used for switching power supplies to remove high-frequency switching transients from the output and sometimes from the feedback to the power input. They usually have an annular ferrite core.

 Some car audio enthusiasts use chokes in car audio systems (especially in subwoofer wiring to remove high frequencies from amplified signals).

 RF choke

 RF chokes (RFCs) usually have iron powder or ferrite cores to increase inductance and overall operation. They are usually wound in a complex manner (basket winding) to reduce self capacitance and proximity effect losses. Chokes for higher frequencies have non magnetic cores and low inductance.

 A modern choke used to eliminate digital RF noise in a line is a ferrite bead, which is a cylindrical or ring-shaped ferrite core that slides over a wire. These are common on computer cables. A typical RF choke value may be 2 MOH.

 Common mode choke

 The common mode (CM) choke wraps two coils around a magnetic core and can be used to suppress electromagnetic interference (EMI) and radio frequency interference (RFI) from the power line and prevent failure of power electronic equipment. It passes differential currents (equal but opposite) while blocking common mode currents. Due to the negative coupling of windings, the magnetic flux generated by differential mode (DM) current in the magnetic core often cancels each other. Therefore, the choke has little inductance or impedance to DM current. In general, this also means that the magnetic core will not be saturated due to large DM current, while XXX rated current is determined by the thermal effect of winding resistance. However, due to the combined inductance of the positive coupling winding, the CM current presents a high impedance.

 Cm chokes are commonly used in industrial, electrical and telecommunications applications to eliminate or reduce noise and related electromagnetic interference.

 When the common mode choke conducts the common mode current, most of the magnetic flux generated by the winding is limited by the inductor core due to its high permeability. In this case, the leakage flux (also the near field emission of the CM choke) is very low. However, the DM current flowing through the winding will produce a high emission near magnetic field, because in this case, the winding is negatively coupled. In order to reduce the near field emission, the twisted winding structure can be applied to the common mode choke.

 An experimental setup for measuring the equivalent current loop and generated magnetic field of CM choke of balanced twisted winding.

 The difference between the balanced twisted pair winding cm choke and the traditional balanced twisted pair winding cm choke lies in the interaction between the windings in the center of the core opening window. When it conducts common mode current, the common mode inductance of balanced twisted winding can provide the same common mode inductance as the traditional common mode inductance. When it conducts DM current, the equivalent current loop will produce a reverse magnetic field in space, so they often cancel each other.

 The current passes through the inductor and the probe measures the near-field emission. The signal generator used as a voltage source is connected to the amplifier. Then connect the output of the amplifier to the measured inductance. In order to monitor and control the current flowing through the inductor, the current clamp is clamped around the wire. An oscilloscope connected to the current clamp is used to measure the current waveform. The probe measures the flux in the air. The spectrum analyzer connected to the probe collects data.

 Well, the above is the introduction to the choke. If you have any questions, please feel free to contact us. If you want to know more about other knowledge, you are welcome to put forward it. We will update the corresponding answers later