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Toroidal transformer is a type of electronic transformer, which has been widely used in household appliances and other electronic equipment with high technical requirements. It’s mainly used as a power transformer and isolation transformer, also widely used in computers, medical equipment, telecommunications, instruments and lighting. The toroidal transformer is a competitive electronic transformer for its good output characteristics and anti-interference ability.
The core of the toroidal transformer is made of high-quality cold-rolled silicon steel sheets (thickness is generally below 0.35mm), seamlessly rolled, which makes its core performance better than traditional laminated cores. The coil of the toroidal transformer is evenly wound on the iron core, and the direction of the magnetic field lines generated by the coil is almost completely coincident with the iron core magnetic circuit. Compared with the laminated type, the excitation energy and core loss will be reduced by 25%. The toroidal core is wound by silicon steel tape, the toroidal core has a continuous magnetic circuit, and the laminated core transformer has an air gap between the EI sheets; therefore, there is a large air gap. The magnetic resistance is laminated The main disadvantage of transformers. The toroidal core has no air gap, and the electrical noise is much smaller than that of the EI and C core transformers. The use of vacuum impregnation technology can make the iron core a solid whole without deformation during winding and processing; because the ring-shaped iron core is very strong, vibration and audio noise are reduced.
The principle of the toroidal transformer is the same as that of the transformer. When a sinusoidal AC voltage U1 is applied to both ends of the primary coil, there is an alternating current I1 in the wire and an alternating magnetic flux ф1 is generated. It passes through the primary coil and the secondary coil along the iron core to form a closed magnetic circuit. A mutual induction potential U2 is induced in the secondary coil, and ф1 will also induce a self-induction potential E1 on the primary coil. The direction of E1 is opposite to the applied voltage U1 and the amplitude is similar, thus limiting the size of I1. In order to maintain the existence of magnetic flux ф1, a certain amount of power consumption is required, and the transformer itself also has certain losses. Although the secondary is not connected to the load at this time, there is still a certain current in the primary coil. This current is called "no-load current" ".
If the secondary is connected to a load, the secondary coil will generate a current I2, and therefore produce a magnetic flux ф2, the direction of ф2 is opposite to ф1, which acts to cancel each other so that the total magnetic flux in the iron core is reduced. The primary self-inductance voltage E1 decreases, and as a result, I1 increases. It can be seen that the primary current is closely related to the secondary load. When the secondary load current increases, I1 increases, and ф1 also increase, and the increased part of ф1 just supplements the part of the magnetic flux offset by ф2 to keep the total magnetic flux in the iron core unchanged. If the loss of the transformer is not considered, it can be considered that the power consumed by the secondary load of an ideal transformer is the electric power obtained by the primary from the power supply.
The transformer can change the secondary voltage by changing the number of turns of the secondary coil as needed, but it cannot change the power that the load can consume.
Both the toroidal transformer and the transformer work using the basic principles of electric-magnetic and magnetic-electric conversion.
The diagram of the working principle of transformers
When the AC current U1 is sent to both sides of a winding resistor L1 of the transformer (the number of coil turns is N1), the AC voltage I1 passes through L1, and L1 immediately creates an electromagnetic field. The magnetic line of the electromagnetic field follows the need for a transformer core with excellent magnetism. Coupling until L2 has wound again (the number of turns of the coil is N2), the induced electromotive force is immediately caused on L2, and then L2 is equal to 1 switching power supply.
Because L2 and load R are combined into a closed circuit, L2 always has AC voltage I2 output and passes through load R, and the working voltage on both sides of R is U2.
One winding of the transformer carries out an electric-magnetic conversion, and the second winding carries out the magnetic-electric conversion.
The main advantages of toroidal transformers are lower radiation fields and higher efficiency. In the case of halving the size and weight, a given capacity can be achieved. If a transformer with a larger capacity is used, the temperature of the transformer can be lowered. The central hole fixing method makes it easy to install the ring-shaped transformer on the printed circuit board. The toroidal transformer has a high degree of flexibility, and the size of the transformer can be designed according to the requirements of the chassis and the overall assembly. Since the production of toroidal transformers does not require a die, nor a coil frame injection mold, the production cycle is short, suitable for small and medium-sized batch production, and can meet the needs of continuous modification of contemporary electronic equipment. Due to the low noise durability of toroidal transformers, many manufacturers use them for high-fidelity audio equipment and video display terminals, power amplifiers, electronic testers, and general equipment.
Toroidal transformers also have some distinguished advantages:
1. High electrical efficiency
There is no air gap in the core, the stacking coefficient can be as high as 95% or more, the core permeability can be 1.5~1.8T (the laminated core can only be 1.2~1.4T), the electrical efficiency is as high as 95%.
2. Small size and lightweight
The weight of the toroidal transformer can be reduced by half compared with the laminated transformer. As long as the cross-sectional area of the core is kept equal, the toroidal transformer can easily change the ratio of the length, width, and height of the core, and the external dimensions can be designed to meet the requirements;
3. less magnetic interference
The toroidal transformer core has no air gap, and the windings are evenly wound on the toroidal core. This structure leads to small magnetic leakage and low electromagnetic radiation. It can be used in high-sensitivity electronic equipment without additional shieldings, such as low-voltage applications. On level amplifiers and medical equipment;
4. less vibration and noise
The iron core has no air gap, so the iron core can be reduced.
Toroidal transformers can be classified into three types: standard type, economic type, and isolated type:
The standard power transformer product series has a capacity of 8～1500VA, a small voltage adjustment rate, and a temperature rise of only 40℃ during full load operation. It allows short-term overload operation and is suitable for high-demand applications. The primary and secondary windings are insulated with Class B (130°C) polyester film. At least three layers of insulating tape are required to withstand the AC 4000V, 1min withstand voltage test.
The economical power transformer product series has a capacity of 50～1500VA and strives to reduce the cost on the basis of guaranteed performance. It is suitable for continuous operation without overloading. The operating temperature rise is 60℃, and the insulation material grade is A grade (105℃ ), when the load is full, the output voltage error is less than 3%.
The capacity of the isolation transformer product series is 50～1000VA, which can be divided into two series for industrial use and medical equipment use. The isolation transformer focuses on its insulation performance. Between the primary and secondary, use Class B insulating polyester film to wrap at least 4 layers, with a breakdown voltage greater than 4000V, and all primary leads must use double insulated wires. The maximum temperature rise of the transformer is less than 45°C. In addition to meeting the above requirements, medical isolation transformers must also meet the UL544 standard, that is, the primary and secondary windings should have thermal protection, and the distance between the winding and the grounded copper shield should be greater than 13mm.
Among the current toroidal transformer products, the most well-known products are the ones used in audio equipment. Such as high-performance products that can be used as power transformers in class 3 high-power high-fidelity amplifiers and power transformers for small and medium power audio equipment. High-quality toroidal transformers can be used in the power range from 6VA to 1000VA.
Electrical control used in current and voltage transformers. High-precision, high-stability transformer made with toroidal transformer technology. New high-performance magnetic materials, such as permalloy soft magnetic materials, amorphous materials, or nanocrystalline alloys, can be used as magnetic cores, equipped with precision smart meters and special testing methods. It can ensure that the transformer parameters are accurate and the performance is completely consistent.
Toroidal transformers specially designed and manufactured for medical equipment. In addition to high efficiency, high reliability, and high safety requirements. It also particularly strengthens the electrical strength and improves the heat resistance. It is required to add a thermal fuse inside the transformer to ensure reliability.
Toroidal transformers can also be used in various power inverters, such as solar and wind power generation systems. This high-efficiency toroidal transformer with a low-loss iron core can greatly improve the overall efficiency of the inverter power supply.
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