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The core application scenarios of toraidal transformers as an alternative to EI transformers
2026-07-04
Ring-shaped low-frequency transformers accelerate the replacement of EI transformers in six core application scenarios
For a long time, EI laminated transformer has dominated the mainstream market for civilian power supplies and ordinary industrial control equipment due to its low production cost, strong shock resistance, and ease of manufacturing multiple windings. However, as the entire equipment continues to evolve towards miniaturization, reduced interference, quieter operation, and higher energy efficiency, the shortcomings of traditional EI transformers have been continuously magnified: significant leakage magnetic field, severe electromagnetic interference, high no-load noise, bulky size at the same power level, and high energy loss.
The toroidal transformer is formed by continuously winding a whole sheet of silicon steel to create a closed magnetic circuit without air gaps. It has lower magnetic resistance, minimal leakage flux, higher conversion efficiency, and a quiet and compact body. With the widespread use of fully automatic toroidal winding equipment, the production cost of toroidal transformers has continued to decline. In many mid-to-high-end industries, they are gradually replacing EI transformers.
The following is a summary by CXWON of the six main paths for implementing the batch replacement of EI products with ring transformers, as well as the replacement logic, performance advantages and implementation conditions for each type of scenario.
- Hi-Fi Audio Amplifiers and Professional Audio Equipment: The Most Mature Alternative Market
Replacing the Status Quo:
The audio industry was the first to complete the upgrade and replacement of EI transformers. From home high-fidelity amplifiers and decoders to stage professional sound equipment and recording studio power supplies, ring transformers have become industry standards. The EI core has largely withdrawn from the mid-to-high-end audio market.
The audio industry was the first to complete the upgrade and replacement of EI transformers. From home high-fidelity amplifiers and decoders to stage professional sound equipment and recording studio power supplies, ring transformers have become industry standards. The EI core has largely withdrawn from the mid-to-high-end audio market.
Core Reasons for Replacement:
First, extremely low leakage magnetic suppression power noise. The EI core has multiple mating air gaps, and the stray magnetic field radiates outward, easily coupling into the signal line, causing AC hum, which is commonly referred to as power noise. The ring closed magnetic circuit can firmly lock the magnetic field inside the iron core, and the external radiated magnetic field is only one-tenth of that of the EI type, effectively eliminating AC interference and significantly improving the signal-to-noise ratio, restoring pure audio signals.
Second, almost no vibration or buzzing during operation. The gap between the silicon steel sheets of the EI laminated plate is large, and under alternating magnetic fields, the magnetostriction vibration is intense. After power-on, it continuously buzzes; the ring iron core is completely tight without joints, and the vibration amplitude is extremely small. The entire machine can achieve nearly silent operation, and will not introduce mechanical noise to the audio system.
Third, more stable voltage output. The load regulation rate of the ring transformer is excellent. Under large dynamic music peaks, the voltage drop is smaller, the transient response speed is faster, and the power output is strong. This is something that the EI transformer cannot achieve.
Selection Boundary:
For single-channel and dual-channel output amplifiers, ring transformers are preferred; for multi-channel low-voltage windings above three channels, due to the limitation of winding process, the cost of ring transformers will increase significantly. Some multi-channel power amplifiers with multiple channels will still retain C-type plug-in iron cores as a compromise solution.
- Medical Diagnostic Instruments: Safety Standards and Low EMI Drive Product Upgrades
Replacing the Status Quo:
Monitoring devices, electrocardiogram equipment, ultrasound diagnostic instruments, portable surgical instruments, and medical isolation power supplies are replacing the original EI (Electrical Isolation) power transformers with ring-shaped isolation transformers in large quantities. This is one of the fastest-growing industries for replacements in recent years.
Monitoring devices, electrocardiogram equipment, ultrasound diagnostic instruments, portable surgical instruments, and medical isolation power supplies are replacing the original EI (Electrical Isolation) power transformers with ring-shaped isolation transformers in large quantities. This is one of the fastest-growing industries for replacements in recent years.
Core Replacement Logic:
1. Strict control of leakage current and electromagnetic radiation. Medical weak electrical equipment is filled with weak biological signal collection circuits. The magnetic field emitted by the EI transformer is prone to causing waveform drift and data distortion. The stray magnetic field of the ring-shaped transformer is extremely low, which does not interfere with the sensor's signal collection and is more likely to pass the medical EMC (Electromagnetic Compatibility) test.
2. Higher isolation safety. The ring-shaped winding arrangement is uniform, the primary and secondary isolation distance is stable, the insulation consistency is better, and the leakage current to ground of the winding can be controlled at the microampere level, meeting the safety requirements for preventing electric shock in medical equipment and ensuring the safety of patient power supply.
3. Smaller and Portable Design Requirements. Under the same power output, the volume of the ring-shaped transformer is reduced by more than 30% and the weight is reduced by nearly half. It is very suitable for portable mobile medical equipment, solving the structural problem of EI transformers being too heavy and not fitting in the chassis.
4. Lower Temperature Rise during Long-Term Continuous Operation. The ring-shaped iron loss and copper loss are smaller, and the body temperature is lower during 24-hour continuous operation. The aging speed of insulation slows down, meeting the reliability requirements of medical equipment for continuous operation without interruption for years.
- Precision Testing Instruments and Laboratory Stable Voltage Power Supply: Pursuing Pure Sine Power Supply
Replacing the Current Situation:
Various signal generators, oscilloscopes, precision DC stable voltage power supplies, chromatography analysis instruments have basically completed the iterative upgrade from EI to ring transformers. The EI transformer outputs a waveform with a large harmonic component and insufficient voltage purity, which can easily cause fluctuations in test data; while the ring transformer has a uniform magnetic path and the output voltage waveform is closer to the standard sine wave, with extremely low harmonic distortion, which can provide high-quality reference power for the measurement system and avoid the influence of power supply noise on measurement accuracy.
Various signal generators, oscilloscopes, precision DC stable voltage power supplies, chromatography analysis instruments have basically completed the iterative upgrade from EI to ring transformers. The EI transformer outputs a waveform with a large harmonic component and insufficient voltage purity, which can easily cause fluctuations in test data; while the ring transformer has a uniform magnetic path and the output voltage waveform is closer to the standard sine wave, with extremely low harmonic distortion, which can provide high-quality reference power for the measurement system and avoid the influence of power supply noise on measurement accuracy.
At the same time, most laboratory equipment is placed inside sealed experimental tables, and noise control is strict. The continuous buzzing of the EI transformer will long-term affect the laboratory environment. The ring transformer, with no vibration structure, can operate silently. In addition, it has a higher no-load efficiency and lower energy consumption in a long-term standby state, resulting in a more favorable overall usage cost.
- Ultra-thin chassis and compact industrial control equipment: Structural substitution due to space constraints
Current situation of substitution
Wall-mounted industrial control power supplies, desktop control hosts, small UPS units, and centralized power supply equipment for building access control systems are all limited by the height of the chassis. Square EI transformers are difficult to be arranged. Flat ring transformers have become the preferred solution.
Wall-mounted industrial control power supplies, desktop control hosts, small UPS units, and centralized power supply equipment for building access control systems are all limited by the height of the chassis. Square EI transformers are difficult to be arranged. Flat ring transformers have become the preferred solution.
Key advantages
The EI core has a square three-dimensional structure, making it difficult to reduce its height; ring transformers can be made in a flat and short structure, significantly reducing the thickness, and perfectly adapting to ultra-thin shells. With the same VA capacity, the overall space occupied by the ring transformer is smaller, and the overall layout is more flexible.
In addition, many control cabinets have compact internal circuit board layouts. Transformers are close to weak current lines. The leakage magnetic field of EI is very likely to cause errors in single chips and communication modules, as well as communication disconnections. After replacing with ring transformers, the stray magnetic field is significantly reduced, without the need for additional shielding covers, which simplifies the structure and reduces the renovation cost.
- Uninterruptible Power Supply, Inverter Isolated Power Supply: High Energy Efficiency Reduces Long-Term Operating Losses
Replacing the Current Situation
Small frequency conversion UPS, photovoltaic auxiliary isolation transformers, and energy storage supporting frequency conversion power supplies gradually eliminate inefficient EI products and shift to the ring configuration. The overall efficiency of ring transformers can reach 92% to 96%, while the efficiency of ordinary EI transformers is mostly between 85% and 90%, and the gap in no-load iron loss is particularly significant. These devices are always in standby and light-load operation states, with 8700 hours of continuous power supply per year. Lower no-load losses can continuously save electricity costs, and over the long term, the savings in energy consumption can bring benefits sufficient to cover the price difference between the ring and EI configurations.
Small frequency conversion UPS, photovoltaic auxiliary isolation transformers, and energy storage supporting frequency conversion power supplies gradually eliminate inefficient EI products and shift to the ring configuration. The overall efficiency of ring transformers can reach 92% to 96%, while the efficiency of ordinary EI transformers is mostly between 85% and 90%, and the gap in no-load iron loss is particularly significant. These devices are always in standby and light-load operation states, with 8700 hours of continuous power supply per year. Lower no-load losses can continuously save electricity costs, and over the long term, the savings in energy consumption can bring benefits sufficient to cover the price difference between the ring and EI configurations.
At the same time, the voltage adjustment characteristics of the ring are more stable, the voltage drop during load is smaller, the inverter output waveform is more stable, which is conducive to improving the stability of the entire power supply system.
- Rail Transit, Vehicle Equipment and Lightweight Electromechanical Products: Essential for Weight Reduction and Volume Reduction
The power supply for vehicle control, auxiliary power supply for high-speed train carriages, and weak current control systems for ships all have strict requirements for the weight of components. The material used for toroidal transformers is more economical, and the utilization rate of the core material is higher. Compared with EI products, it can reduce weight by up to 40%, effectively lowering the overall weight of the equipment and reducing the load on the vehicle body.
The space for vehicle equipment is limited, and the components are densely arranged. The electromagnetic radiation of EI transformers is prone to interfere with the vehicle bus communication. The closed magnetic circuit of the toroidal transformer has a natural shielding effect, providing stronger anti-interference ability, which can reduce the workload of vehicle EMC rectification and shorten the project development cycle.
- Objective Boundaries: Scenarios Where EI Transformers Cannot Be Completely Replaced in the Short Term
We should also view industrial evolution rationally. The ring structure will not completely eliminate the EI products. In the following scenarios, the EI still maintains an unshakable advantage:
1. Large quantities of low-end civilian products (ordinary monitoring power supplies, LED lighting transformers), cost priority, the production unit price of EI laminated plates is lower;
2. Multi-channel and multi-winding output products, the EI frame winding process is simple, multiple windings are easier to control the safety creepage distance;
3. Motor load equipment with DC components and frequent surge impacts, the EI has its own air gap, has stronger resistance to DC bias magnetization, and is less likely to experience magnetic saturation;
4. Power distribution transformers above 5kVA for large-scale industrial use, the internal heat dissipation conditions of the ring structure are poor, and full-load sealing is prone to heat accumulation, large-power models still mainly use EI and C-type plug-in iron cores.
1. Large quantities of low-end civilian products (ordinary monitoring power supplies, LED lighting transformers), cost priority, the production unit price of EI laminated plates is lower;
2. Multi-channel and multi-winding output products, the EI frame winding process is simple, multiple windings are easier to control the safety creepage distance;
3. Motor load equipment with DC components and frequent surge impacts, the EI has its own air gap, has stronger resistance to DC bias magnetization, and is less likely to experience magnetic saturation;
4. Power distribution transformers above 5kVA for large-scale industrial use, the internal heat dissipation conditions of the ring structure are poor, and full-load sealing is prone to heat accumulation, large-power models still mainly use EI and C-type plug-in iron cores.
The essence of the substitution trend is the upgrade of the overall machine demand.
The replacement of ring transformers and EI transformers is not a simple structural substitution. It is an inevitable result driven by the three major demands of the entire machine equipment: miniaturization brings the demand for weight reduction and volume reduction, electromagnetic compatibility requirements force the adoption of low leakage magnetic schemes, and long-term energy saving promotes the popularization of low-loss cores.
In the six major sectors of audio equipment, medical instruments, precision testing power supplies, ultra-thin chassis industrial control, small uninterruptible power supplies, and vehicle lightweighting equipment, ring transformers have demonstrated a trend of large-scale substitution due to their four core advantages: low leakage magnetic field, quiet operation, high efficiency, and compact size. With the widespread use of fully automatic ring winding machines and the continuous improvement of winding production efficiency, the penetration rate of ring transformers in the medium and high-end power supply market will continue to rise in the future.
For R&D selection personnel, single and double winding, emphasis on interference and noise, compact space, and projects requiring long-term continuous operation can prioritize the use of ring transformers; for multi-winding, impact loads, and cost-optimized large-scale civilian products, the EI laminated sheet solution will continue to be retained, each playing its own role, forming a long-term complementary industrial pattern.
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