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    Toroidal Transformer: Definition, Working Principle and Advantages

    A transformer is an electrical device that is used to transfer electrical energy from one circuit to another circuit through electromagnetic induction. It consists of two coils of wire, known as primary and secondary coils, which are wound around a common magnetic core.

    There are many kinds of power transformer, toroidal transformer is one of them. In this atricle, ATO automation will introduce some basic knowledge of toroidal transformer.

    300 VA toroidal transformer


    A toroidal transformer is a type of electrical transformer that has a toroidal (doughnut-shaped) core made of a ferromagnetic material, such as iron powder or silicon steel. The primary and secondary coils of wire are wound around the core, with the primary coil connected to the input voltage source and the secondary coil connected to the output load.

    One of the main advantages of a toroidal power transformer is its compact size and shape, which allows for efficient use of space in electronic equipment. The toroidal shape also reduces the amount of magnetic flux leakage, which can cause electromagnetic interference with other components in the equipment. This results in a transformer with high efficiency, low noise, and low electromagnetic radiation.

    Working Principle:

    Toroidal transformer working principle

    Electrical transformers operate based on Faraday's law of induction. This physical law states the relationship between the rate of change of a magnetic flux and the induced electromotive force. A magnetic flux is created when magnetic field lines pass through a conductor. It was observed that placing a conductor near a magnetic field with varying amplitude generates an electric current in that conductor.

    The magnetic field involved in electromagnetic induction is typically from an electromagnet with a varying electric current. This varying electric current is commonly known as alternating current (AC). As the electrical current is generated and collapsed continuously at a given frequency, the magnetic field is also created and collapsed the same way. This magnetic field with varying amplitude induces an electric current to a second conductor. The induced electrical current in the second conductor has the same frequency as the electrical current from the electromagnet circuit.

    A magnetic field with varying amplitude is not the only way to induce a current. A magnetic field can be imagined as a field with many lines of induction. Making the conductor "cut" through these magnetic field lines can generate an electric current.


    • Volume and weight. All windings in a toroidal transformer are symmetrically spread over the entire core which makes the wire length very short. A higher flux density is also possible as the magnetic flux is in the same direction as the rolling direction of the grain-orientated core, allowing significant savings of volume and weight. A higher current density can flow through the wire as the whole surface of the toroidal core allows efficient cooling of the copper windings. This smaller size makes it more useful for compact electrical products.
    • Efficiency. The ideal magnetic circuit of the toroid, reduces the number of turns of wire required and/or the core cross-sectional area. Either benefit reduces losses.
    • Transformer hum. Audible hum is caused in transformers when the windings and core layers vibrate due to the forces between coil turns and core laminations. Moreover, the hum increases over time as the laminations start loosening. But the construction of toroidal transformers helps to dampen acoustic noise. The core is tightly wound, spot welded, annealed, and coated with epoxy resin or insulated with Mylar tape. The uniform winding of the core leaves no air gaps, thus leaving no loose sheets to vibrate, ultimately resulting in less hum.
    • Stray field. Stray field in toroidal transformers is approximately 85-95% lower than in conventional laminated transformers. Achieving low levels of stray field is an important consideration for the equipment designer as the phenomenon can create unwanted noise through interference with sensitive electronics. A toroidal transformer will generally offer a reduction of 8:1 in magnetic interference levels compare with traditional frame style laminate types.
    • Dimensional flexibility. Toroidal transformers offer a high degree of dimensional flexibility compared with conventional laminated transformers. Toroidal cores can be produced in virtually any diameter or height.
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