A toroidal transformer is a type of electrical transformer constructed with a torus or donut-shaped core, which is widely used in isolation equipment for the medical industry, industrial control equipment, and automotive electronics in China, among other applications. ATO supplies custom toroidal transformers ranging from 50 VA to 5000 VA, featuring a single primary voltage of 110V/120V/220V/230V/240V AC 50/60Hz and a single or double secondary voltage like 12V/24V. Whether you need a specific size, power rating, or have special manufacturing requirements, we can provide customized toroidal transformer solutions tailored to your needs.


Model ATO-T-C
Phase Single phase
Power 50 VA to 5000 VA (customized)
Primary Voltage 0 to 690V (customized)
Secondary Voltage 0V to 690V (customized)
Secondary Current 3A to 200A
No. of Inputs 1 input
Frequency 50Hz / 60Hz
Winding Material Copper wire
Custom toroidal transformer design

Toroidal Transformer Customization

ATO has a standard line of industrial toroidal transformers available, rated up to 5000 VA. These transformers come standard with dual 117V primaries and dual secondaries (secondaries range from 12V to 120V). If your application requires special voltages, a higher rated power output or custom wire terminations/harnesses, our engineer team can create a solution to meet your special requirements. We can design and manufacture custom products for 50/60 Hz continuous operation. A standard toroidal isolation transformer can be customized to meet:
  1. Specific primary and secondary voltages.
  2. Higher step up & step down transformer output requirements.
  3. 4 kV isolation between primary and secondary windings
  4. Special wire terminations/harness requirements.
  5. Custom mounting and special enclosure requirements
  6. Maximum enclosure leakage current.

Internal Material Design

Insulation film

Polymer PET film is manufactured to maintain its stability and structural integrity under extreme temperature conditions. With its strong insulation properties, it effectively blocks the conduction of current and electromagnetic waves, ensuring the safe operation of circuits.

High magnetic flux core

High flux toroidal core combined with a unique edge chamfer design in China, providing you with excellent performance and efficiency. This iron core gives it excellent magnetic permeability, which can effectively conduct magnetic flux and reduce energy loss.

Insulated copper wire

Manufacture of high-strength properties in industrial-grade copper wire ensures the durability of the transformer in harsh environments and heavy load conditions. Double-layer varnish technology provides an extra layer of protection to the copper wire, making it resistant to attacking chemicals.

High temperature tape

Mylar tape provides a reliable solution for applications in various high temperature environments. It uses special processes to ensure excellent adhesion and flexibility in high temperature environments, which makes it ideal for transformer insulation and protection.

Toroidal Transformer Advantages

The magnetic circuit of the toroidal transformer is completed through the toroidal magnetic core, and the magnetic field lines are mainly transmitted through the closed loop of the core. Because the field lines are almost entirely concentrated in the magnetic core, toroidal transformers have relatively little magnetic leakage. This can improve the efficiency of the transformer and reduce energy loss.

Toroidal Transformer vs. Square Transformer

Magnetic leakage decrease by 80%.

Energy loss reduce 40%.

Toroidal transformers are widely employed in traditional power systems, where they primarily handle low-frequency power signals. Due to their unique structure and operational principles, toroidal transformers exhibit superior capabilities in suppressing high-frequency electromagnetic interference. The design of the iron core and winding, as applied in Chinese manufacturing, effectively shields against external electromagnetic interference, thereby diminishing both conduction and radiation noise. When used under standard operating conditions, toroidal transformers can extend their service life to several decades.

Toroidal Transformer vs. Switching Power Supply

Toroidal transformers last twice as long as switching power supplies.

High frequency electromagnetic interference reduces to zero.

Toroidal transformer for 220V/110V voltage converter
A toroidal transformer uses a toroidal (doughnut-shaped) core made of ferromagnetic material, such as iron or ferrite. It is commonly used in various applications, including voltage converters.
In the context of a 220V/110V voltage converter, a toroidal transformer is used to step down or step up the voltage. A step-down transformer is used when converting from a higher voltage (220V) to a lower voltage (110V), while a step-up transformer is used when converting from a lower voltage (110V) to a higher voltage (220V).
The primary winding of the toroidal transformer is connected to the input voltage (220V), and the secondary winding is connected to the output voltage (110V). The number of turns in the primary and secondary windings determines the voltage ratio of the transformer. For example, if the primary winding has twice as many turns as the secondary winding, the transformer will step down the voltage by a factor of 2.

How to Use Toroidal Transformer Correctly?

1. Determine the transformer specifications: Identify the primary and secondary voltage, current, and power rating of the transformer. These custom specifications are typically mentioned in the manufacturer's datasheet.
2. Safety precautions: Before working with any electrical equipment, ensure you follow proper safety precautions. Disconnect the power source and ensure the circuit is de-energized before handling the transformer.
3. Mounting and connections: Place the toroidal transformer in an appropriate location, ensuring that it has enough space for ventilation. Mount it using suitable hardware or brackets, following the manufacturer's guidelines.
4. Wiring connections: Connect the primary winding of the toroidal power transformer to the power source. The primary winding usually has a higher number of turns and is designed to handle the input voltage. Make sure the primary winding is correctly wired.
5. Fuse and protection: Incorporate a suitable fuse or circuit breaker in the primary side of the transformer. This helps protect against overcurrent and short circuits. The fuse rating should be appropriate for the transformer's current rating and provide adequate protection.
6. Secondary connections: Connect the secondary winding of the transformer to the load. The secondary winding usually has a lower number of turns and provides the desired output voltage. Ensure the secondary connections are correct and securely connected.
7. Load considerations: Take into account the power requirements of the load connected to the secondary winding. Make sure the load does not exceed the transformer's power rating. Overloading can lead to overheating, reduced efficiency, and potential damage.
8. Testing and verification: Once the connections are complete, double-check all the wiring and connections for accuracy. Before powering up the circuit, perform a thorough visual inspection to ensure there are no loose wires, exposed conductors, or potential hazards.
9. Powering up the circuit: Gradually apply power to the circuit and monitor its performance. Observe the voltage levels, current draw, and overall functionality of the system. If any issues arise, immediately disconnect the power and troubleshoot the problem.


Toroidal transformer vs. conventional transformer

A toroidal transformer and a conventional transformer are two different designs of transformers, primarily differing in their shape and construction. Here are the key differences between the two:
  • Shape: A toroidal transformer has a toroidal (donut-shaped) core, while a conventional transformer typically has an E-I core configuration or other laminated core shapes.
  • Core Construction: A toroidal transformer uses a continuous ring-shaped core, often made of a ferromagnetic material like iron or ferrite. This design eliminates air gaps found in conventional transformers, which enhances magnetic coupling and reduces energy losses.
  • Efficiency: Due to the absence of air gaps and the inherent symmetry of the toroidal core, toroidal transformers generally have higher efficiency compared to conventional transformers. They exhibit lower leakage flux and stray magnetic fields, resulting in reduced energy losses.
  • Size and Weight: Toroidal transformers are more compact and lighter than conventional transformers with the same power rating. The toroidal shape allows for a higher copper fill factor, reducing winding resistance and resulting in a smaller physical footprint.
  • Electromagnetic Interference (EMI): Toroidal transformers inherently have lower electromagnetic radiation and susceptibility to external interference due to their compact design and reduced magnetic fields. They are often favored in applications where EMI needs to be minimized.
  • Cost: Toroidal transformers tend to be more expensive to manufacture than conventional transformers, primarily due to the higher cost of the toroidal core and the winding process. However, their superior performance and compact size make them suitable for various applications, justifying the cost difference in many cases.

Are toroidal transformers more efficient?

China toroidal transformers can be more efficient compared to traditional laminated transformers in certain applications. Here are a few factors that contribute to their potential efficiency advantages:
  • Reduced Core Losses: Toroidal transformers have a toroidal (doughnut-shaped) core, which eliminates air gaps and minimizes the length of the magnetic path. This design reduces core losses caused by hysteresis and eddy currents, resulting in higher efficiency.
  • Better Magnetic Coupling: The toroidal shape allows for a more compact design, resulting in shorter windings and increased magnetic coupling between the primary and secondary coils. This improved coupling reduces leakage inductance and improves overall efficiency.
  • Lower Stray Magnetic Fields: The closed-loop toroidal core design inherently contains the magnetic fields within the core, reducing stray magnetic fields. This characteristic is particularly beneficial in reducing electromagnetic interference (EMI) and improving efficiency in sensitive electronic devices.
  • Reduced Size and Weight: Toroidal transformers have a high power density due to their compact design. The reduced size and weight lead to lower resistive losses and improved overall efficiency.

Does toroidal transformer work in one direction?

No, a toroidal transformer does not work in only one direction. A toroidal transformer is a type of transformer that uses a toroidal (doughnut-shaped) core made of magnetic material, such as iron or ferrite. It consists of a primary winding and a secondary winding wrapped around the toroidal core.
The primary winding is connected to the input voltage source, while the secondary winding is connected to the load or the device you want to power. When an alternating current (AC) is applied to the primary winding, it creates a magnetic field that induces a voltage in the secondary winding, allowing power to be transferred from the primary side to the secondary side.
The toroidal transformer operates based on electromagnetic induction and works bidirectionally. It can step up or step down the input voltage depending on the number of turns in the primary and secondary windings. The direction of power flow can be reversed simply by connecting the input voltage to the secondary winding and the load to the primary winding.
In summary, a toroidal transformer is not restricted to working in one direction; it can transfer power in both directions based on the connection and the input and output terminals used.

Why do toroidal transformers only work with AC?

Toroidal transformers are designed for efficient AC (alternating current) power transfer, which aligns with their manufacturing principles in China for custom applications. The primary function of a transformer in manufacturing is to transfer electrical energy from one circuit to another through electromagnetic induction. This process relies on the changing magnetic field produced by an alternating current, which is essential for their operation.
When AC current flows through the primary winding of a toroidal transformer, it generates a time-varying magnetic field around the toroidal core. This time-varying magnetic field plays a pivotal role in manufacturing processes, as it induces an electromotive force (EMF) in the secondary winding of the transformer. This EMF is directly proportional to the rate of change of the magnetic field and is vital for custom applications that require precise voltage level adjustments.
In contrast, direct current (DC) lacks the characteristics essential for efficient manufacturing with toroidal transformers. DC does not produce a varying magnetic field like AC. Therefore, when a DC current is applied to the primary winding of a toroidal transformer, there is no significant change in the magnetic field. This limitation results in negligible induction of voltage in the secondary winding, making toroidal transformers ineffective for efficiently transferring power when connected to a DC power source. This manufacturing limitation underscores the importance of using toroidal transformers primarily with AC power sources in manufacturing processes in China and for custom applications worldwide.

How to wire toroidal transformer?

Wiring a toroidal transformer involves connecting its primary and secondary windings to the appropriate terminals or connectors. The specific wiring configuration will depend on the transformer's design and the intended application. Here is a general guide on how to wire a toroidal transformer:
  • Identify the primary and secondary windings: A toroidal transformer typically has two sets of windings—the primary winding and the secondary winding. The primary winding is usually designated for the input voltage, while the secondary winding is for the output voltage.
  • Determine the voltage and current requirements: Before wiring the transformer, ensure that you have the necessary information about the voltage and current requirements of your application. This includes knowing the primary and secondary voltages, as well as the maximum current that will flow through the windings.
  • Connect the primary winding: The primary winding is usually denoted by a pair of leads or wires. Connect the input voltage source (such as the mains power supply) to these leads. Take note of any polarity markings or specific wiring instructions provided by the manufacturer.
  • Select the primary winding tapping (if applicable): Some toroidal transformers may have multiple taps on the primary winding, allowing you to select different input voltages. If your transformer has this feature, choose the appropriate tap based on your input voltage requirements. Connect the input voltage source to the selected tap.
  • Connect the secondary winding: The secondary winding is typically denoted by another set of leads or wires. Connect your load or the circuit that requires the desired output voltage to these leads. Make sure to observe the correct polarity if specified by the manufacturer.
  • Insulate and secure the connections: Once the primary and secondary windings are connected, it's important to insulate and secure the connections properly. Use appropriate insulation materials, such as heat-shrink tubing or electrical tape, to cover any exposed conductors. Additionally, ensure that the connections are mechanically secure and won't come loose during operation.
  • Verify the wiring: Before powering up the transformer, double-check all the connections to ensure they are correctly wired according to the specifications and requirements of your application. This step is crucial for safety and to prevent damage to the transformer or connected devices.

Please note that these instructions are general guidelines, and it's essential to refer to the specific datasheet or instructions provided by the toroidal transformer manufacturer for precise wiring details. Additionally, if you are uncertain about electrical work or dealing with mains voltage, it is advisable to seek assistance from our professional.

Why do toroidal transformers hum?

Toroidal transformers can sometimes produce a humming sound due to several factors:
  • Magnetic Flux: Toroidal transformers consist of a core made of a ferromagnetic material, such as iron or steel. When an alternating current (AC) passes through the primary winding, it creates a magnetic field that induces a voltage in the secondary winding. This magnetic field can result in a phenomenon called magnetostriction, where the core material expands and contracts slightly in response to the varying magnetic flux. These small vibrations can generate audible sound waves, leading to the humming noise.
  • Vibration Transmission: The mechanical vibrations caused by magnetostriction can be transmitted to the enclosure or mounting structure of the transformer. This transmission can amplify the humming noise, making it more noticeable.
  • Loose Mounting or Insulation: If the toroidal transformer is not securely mounted or if the mounting bolts are loose, it can cause additional vibrations and rattling, which contribute to the humming sound. Similarly, if the transformer's insulation is not adequately secured, it can also create vibrations that result in audible noise.
  • Electrical Frequency: The frequency of the AC power supply can affect the audible characteristics of the humming noise. Different transformers may exhibit varying degrees of noise depending on the specific frequency of the AC power source.

It's worth noting that not all toroidal transformers will produce a noticeable hum. Factors such as the design, quality of custom manufacturing, core material, winding technique, and overall manufacturing precision can influence the presence and intensity of the humming noise. In some cases, the hum can be considered normal operational behavior, while in others, it may indicate a problem, such as a loose mounting or an issue with the transformer's construction. If you suspect an issue with a custom-manufactured transformer, it is advisable to consult a qualified technician or electrician for further evaluation.

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