October 9, 2015

What are Toroidal Transformers and How do They Work?

CET Technology designed a unique toroidal transformer to meet client’s pinout specification.  Typical toroidal transformers might have a total of four connections, two for the input and two for the output. The customer had a need for a total of 18 connections at precise locations for mounting on to the printed circuit board.  As shown in the photograph below, this part has a very unique pin layout. The toroidal transformer also has an unusually large number of windings, 9 in total.  The challenge was to design the component such that it could be manufactured on a production scale with precision and reliability. CET was successful in meeting the distinctive and demanding requirements.

 

Toroidal TransformerHow a Toroidal Transformer Works

A transformer is an electric device which converts the voltage of an alternating current (AC) from one value to another. Step up transformers increases the voltage whereas step down transformers decreases the voltage. Usually, a transformer is constructed by winding coils around a magnetic core of high magnetic permeability.

 

Toroidal Cores

A Toroidal transformer differs from ordinary transformer due to its shape of the core and the properties attained by such a shape. Basically, a toroidal transformer has a doughnut-like shape. A coil made up of insulated wire is wound up around a circular ring-shaped magnetic core to construct the toroidal transformer.

Further Reading:

Similar to any other transformer, the toroidal transformer also has a primary and a secondary coil. The input to the toroidal transformer is connected to the primary coil. As the electric current starts to pass through this toroidal coil, a varying magnetic field is induced in the toroidal core. The strength of the induced field depends on the instantaneous value of the input AC current. As the amplitude of the AC sine wave increases, the field intensity also increases.

The magnetic field induced by the primary coil reaches the secondary coil and then it will result in the production of alternating current in the secondary coil. Thus, the electricity is passed on from the primary coil to the secondary coil without actually having any physical contact.

The core of the transformer is constructed in a way to make the contraction of magnetic fields better. The toroidal core will look like a doughnut and may be made of ferrite, powdered metal, or tightly wrapped strips of steel, wound very tightly like a clock spring.

The main reason for magnetic flux leakage in ordinary transformers is the air gap in the core. In an ideal condition, there should be no air gap in a magnetic circuit. Due to the specialty in construction, there is no air gap in a toroidal transformer’s core. The coils are wound uniformly over the core allowing the machine to work at a relatively higher flux density than ordinary transformers. Also, the natural magnetic screening effect combined with the air gap elimination will reduce the leakage of the magnetic field.

 

Advantages and applications of Toroidal Transformers

The use of toroid shaped cores has increased in recent years. Toroidal transformers have relatively higher efficiency. The humming noise produced by the toroidal transformer is also very low.

Due to its round shape, the magnetic field created by toroidal transformer stays inside it causing less interference with nearby circuits and avoids the energy generated from being captured by adjacent objects. Toroidal coils also have the ability to reduce winding resistance.

The donut shape of toroidal transformers results in lower magnetic field leakage.  The reason is that magnetic fields naturally tend to follow a smooth closed path. Sharp corners and gaps tend to result in a leaked magnetic field.  But a toroid presents a constant turn radius naturally suited to contain magnetic fields.

In addition, toroidal transformers have the longest winding window of any core shape.  The winding window is the length of the toroidal core that is available to be wrapped by the coil windings. For toroids, it is the entire length of the core. For EI transformers, it is only the length of the center leg. The long winding window is important because it also improves efficiency.

For EI transformers, it is necessary to wind one layer of turns on top of another to get all the required turns in the winding window. Any amount of space between any turn and the core results in higher losses because it represents a space that a magnetic field can leak out of. For toroids, it is generally possible to get every winding turn directly onto the core, again reducing magnetic field leakage and improving efficiency.

Toroidal cores are used in a wide range of applications like high-frequency coils and transformers.

Contact CET Technology to discuss Toroidal Transformer requirements:  cet@cettechnology.com