Toroidal coils, first and foremost, are different in terms of shape, when compared to any other types of coils. They are doughnut or ring-shaped coils, which have a doughnut-shaped core, around which wire is wound. The wire is repeatedly taken through the central hole and wrapped back around the outside. It is this mechanism of building the wire-packed core that gives toroidal coils the shape they possess; unlike other coils that are cubic or rectangular in shape. In cubic or rectangular shaped coils, wire is wrapped around a bobbin, having a set of cores fitted through the center and around the outside of the bobbin.
Because of the different shape of the coil, toroidal coils need a specialized process to be followed to manufacture them. They do not have standard mounting like other coils. Their connections are flying leads, while smaller coils can be mounted on bases that allow easy insertion into PCBs.
The main advantage of a toroidal coil is that the shape of the core reduces the amount of magnetic flux escaping from it; thus making the core a closed loop. The core does not have ends or corners from where the magnetic flux can escape, thus reducing losses, leading to greater efficiency and lesser electromagnetic interference. Moreover, the windings in this kind of coil can be distributed around the whole core, giving a better utilization of the core material and better coupling between separate windings, which results in maximum efficiency. Also, the closed loop gives higher magnetic field, higher inductance, and Q factor. This increased efficiency can help to obtain more power, which can be utilized in mains power transformer applications. The industry that gained maximum benefits with the use of toroidal coils was the audio industry, which saw benefits due to reduced distortion and fringing effects that produced a cleaner sound.
The two most common types of toroidal chokes are common mode chokes and differential mode chokes, which are both used for blocking of unwanted frequencies or interference. The common mode chokes utilize the toroidal shape by putting two windings on one core, where the windings can cancel out the interference as they are wound in different directions. The windings are of insulated material; each put in series with one of the conductors. The magnetic fields thus combine to present high impedance to the noise signal. The desired signal passes through the coil, while blocking out the noise component, resulting in high reactance of the inductor. This choke has low electrical resistance that allows for minimal power loss; and high inductance to maximize the attenuation of the noise signal. These common mode chokes are effective only when the desired currents are equal and opposite on two separate conductors, and their reactance is only effective to the noise signal. However, filtering of noise from a single conductor requires a differential mode choke.
Miracle Electronics is one toroidal transformer in Germany where you can get the finest quality toroids that are RoHS and REACH compliant, and are also available with CE and UL marks if required.