* Product Parameters
Operating frequency:10kHz-500KHz Operating temperature:-40℃ to +125℃ Storage temperature:-25℃ to +85℃ Storage humidity:30 to 95%
* Features EE28 transformer isDurable, cost-effective, and flexible in designSolutions for small and medium power magnetic components. Its core advantage lies in...Mature industrial chain and manufacturing process,as well asGood applicability in flyback topologies.
* Typical application areas
* Product Standards UL, RoHS, 3C,CQC
* Size Specifications 
Type | Structure
Tурe | Dimension（mm） | Pin Row （mm） | Row Pitch（mm） | OD Pin（mm） | note | A | B | C | Pin | E | F |
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| EE28-001 | Vertical | 29.0 | 22.0 | 21.0 | 5+5 | 5.0 | 17.5 | Φ0.80 |
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The above are commonly used skeleton styles for companies.,Other styles are not included.,Inquiries are welcome. Our company can customize high-frequency transformers of various specifications according to customer requirements.
EE28 Transformer The EE28 transformer is a high-power, high-frequency transformer. Compared to the EE25 and smaller models, its core effective cross-sectional area (Ae) and window area (Aw) achieve a significant leap, greatly enhancing power handling capability, thermal stability, and interference resistance. Its core electrical performance is determined by the core material, winding technique, topology scheme, and heat dissipation system, making it suitable for 80–200W high-power supply scenarios. The following analysis covers core parameters, key performance influencing factors, and optimization directions. I. Core Electrical Performance Parameters (Baseline Conditions: 100kHz, LLC Resonant Topology) Parameter Category | Key Indicators | Typical Value / Range | Explanation | Basic Electromagnetic Parameters | Inductance (L) | 2mH–50mH | Determined by core AL value, turns, and air gap; tolerance ±1% to ±3%; high air gap adjustment precision, suitable for high-power topologies. | Leakage Inductance (Lk) | 0.3%–1.0% of L | Under same process, leakage inductance is much lower than medium and small cores, significantly reducing voltage spikes and simplifying EMI filter design. | DC Resistance (DCR) | Primary: 0.08–1.5Ω;
Secondary: 0.02–0.6Ω | Very large window area allows for large wire diameter or multiple parallel strands, resulting in better copper loss control. | Loss & Efficiency | Core Loss (Pc) | 500–1200mW | Increases with frequency/flux density; N97 material's high-frequency loss is over 25% lower than N87, with excellent high-temperature resistance. | Copper Loss (Pcu) | 600–1800mW | Affected by current density/winding process; Litz wire effectively suppresses skin effect above 200kHz. | Efficiency (η) | 93%–98% | Higher efficiency than EE25 at equivalent power; full-load efficiency in LLC topology can exceed 97%. | Safety & Insulation | Isolation Withstand Voltage | Primary-Secondary:
5–8kV AC/1min | Bobbin barrier height ≥10mm, creepage distance ≥8mm, meeting medical Class B and heavy-duty industrial equipment safety standards. | Insulation Resistance | ≥2000MΩ (500VDC) | Excellent moisture and salt spray resistance, suitable for outdoor and high-humidity industrial environments. | Thermal Performance & Endurance | Operating Frequency | 5kHz–500kHz | Very low saturation risk at low frequencies, controllable high-frequency loss, covering scenarios from power frequency critical points to high-frequency switching supplies. | Output Power | 80–200W | 120W with natural convection; up to 200W with heatsink and forced air cooling. | Operating Temperature | -40℃~+200℃ | Compatible with Class H (180℃) and Class C (220℃) insulation systems; full-load temperature rise ≤60℃. |
II. Key Factors Affecting Performance 1. Core Characteristics: Core Support for High-Power Handling Advantage of external span A=28mm: Effective cross-sectional area (Ae) increases by approximately 60% compared to EE25, geometrically enhancing flux handling capability, making core saturation risk under high-current conditions almost negligible. The significantly larger window area (Aw) can accommodate both large-diameter windings and multi-layer insulation structures, meeting the design needs for high inductance, low copper loss, and high insulation. Air Gap Design: Optimal air gap range is 0.5–2.0mm.
Forward Topology: Requires a very small and uniform air gap (0.5–1.0mm) to ensure fast core reset.
Flyback Topology: The air gap can be increased (1.2–2.0mm) to significantly boost saturation current and overload capability.
LLC Resonant Topology: Requires precise air gap grinding to ensure high matching between magnetizing inductance and resonant parameters, reducing resonant loss.
Material Selection:
N97: Suitable for high-frequency, high-power scenarios (50–500kHz), offering low loss, high permeability, and high-temperature resistance. Preferred for industrial inverters and energy storage power supplies.
3C94: Suitable for 200–500kHz, offering balanced cost-effectiveness, ideal for consumer electronics high-power adapters.
PC44: Suitable for 50–200kHz, lower cost, suitable for cost-sensitive, high-volume industrial applications.
2. Winding Design: Key to Losses and Stability Turns Ratio & Wire Gauge: The turns ratio determines the voltage conversion ratio. For 80–200W supplies, primary wire diameter is recommended at 0.8–1.5mm, secondary at 1.5–2.5mm. For high output current, the secondary uses 5–10 parallel strands of 0.8mm wire to maximize suppression of skin and proximity effects. Winding Technique: Using interleaved winding (e.g., primary-secondary-primary-secondary) plus a double-layer copper foil shield can control leakage inductance to within 0.5% of the main inductance. A dual insulation layer of Nomex paper and polyimide tape between primary and secondary meets high isolation withstand voltage requirements. For high-frequency operation, use Litz wire with strand diameters of 0.15–0.25mm, reducing high-frequency copper loss by 35–45%. Insulation Design: Inter-layer insulation thickness ≥0.2mm, primary-secondary creepage distance ≥8mm, meeting safety standards like UL60601-1 (medical) and UL508C (industrial control equipment), suitable for high-reliability, high-power scenarios. 3. Topology Matching: Core to Efficiency and Reliability
LLC Resonant Topology: Suitable for 120–200W high-efficiency power supplies, efficiency can exceed 97%. The low leakage inductance of EE28 reduces resonant circulating current loss and improves system dynamic response, making it the preferred topology for energy storage and server power supplies.
Forward Topology: Suitable for 80–120W low-ripple power supplies, requiring an active clamp circuit. The large Ae reduces flux density, decreasing core loss, suitable for precision industrial control power supplies.
Flyback Topology: Suitable for 80–100W cost-sensitive solutions. Compared to EE25, it can use fewer turns and larger wire diameter, further reducing copper loss and enhancing short-term overload capability (can withstand 150% rated load).
4. Operating Conditions: Ensuring Long-term Stable Operation
Frequency: Core loss is proportional to the square of frequency. When frequency exceeds 300kHz, prioritize low-loss materials like N97 or 3C94. When frequency is below 10kHz, flux density should be further reduced to avoid core saturation.
Temperature: High temperature reduces permeability and increases losses. Ensure core operating temperature does not exceed the Curie temperature (~240℃ for N97). Using thermal grease + aluminum heatsink + forced air cooling system can reduce temperature rise by 20–30℃.
Load Rate: Optimal efficiency typically occurs at 80–95% load. Under light load (<20%), optimize winding distributed capacitance to reduce standby loss to below 80mW.
III. Performance Optimization Suggestions
Material Optimization: Use N97 instead of 3C94 for high-frequency, high-power scenarios; choose N27 for high-temperature industrial scenarios; PC44 can be used for cost-sensitive consumer electronics.
Winding Optimization: Mandate the use of Litz wire for frequencies ≥200kHz. Employ interleaved winding + double-layer copper foil shielding to control leakage inductance within 0.5%.
Thermal Optimization: Apply thermal conductive coating on the core surface and attach a large-area heatsink. Design an independent forced air cooling duct with wind speed ≥2m/s to improve forced convection cooling efficiency.
Parameter Matching: For LLC topology, prioritize magnetizing inductance accuracy (tolerance ±1%). For Forward topology, reduce the air gap and match active clamp parameters. For Flyback topology, increase the air gap to enhance saturation resistance.
Characteristics of EE28 Transformer I. Core Advantages and Characteristics Balance of Power and Size The EE28 is a classic medium-to-high-power core. The product of its effective cross-sectional area (Ae) and window area (Aw), known as the AP value, makes it suitable for 80–200W high-power supply scenarios, as well as for handling corresponding power levels in DC-DC converters. Within this power range, it achieves an excellent balance between volume, thermal performance, and cost.Robust Structure, Easy to Manufacture
Standardization & Versatility: The EE28 is an industry-standard size, produced by all major magnetic material manufacturers (TDK, Ferroxcube, etc.). Matching components like bobbins and core clamps are readily available.
Easy Winding and Assembly: The E-core's bobbin is separate, facilitating complex designs with multiple windings and taps (e.g., multioutput flyback transformers). The two core halves are assembled and can be secured with clamps or tape. The production process is mature and highly automatable.
Good Thermal Structure: The E-core offers a relatively large contact area with the windings. Both the center leg and side legs provide heat dissipation paths, aiding the transfer of heat from the windings to the core and then to the environment.
Flexible Inductance Design (For Flyback Topology)
Facilitates Air Gap Implementation: For a flyback transformer (essentially a coupled inductor), an air gap must be introduced into the magnetic path to prevent saturation due to DC bias. For E-cores, the air gap can be conveniently created on the center leg (by grinding or using a gap spacer), a process that is mature and controllable.
Energy Storage Capability: Introducing an air gap allows the core to store more energy without saturating, which is precisely what a flyback transformer requires. The air gap size can be precisely adjusted to achieve the desired primary inductance (Lp).
Good High-Frequency Adaptability When appropriate ferrite materials (such as PC40, PC44, PC95) are selected, the EE28 transformer can operate efficiently from several tens of kHz up to several hundred kHz. This meets the requirements for high-frequency operation and miniaturization in modern switch-mode power supplies.
Typical Application Scenarios of EE28 Transformer Leveraging its high-power capacity and excellent stability, the EE28 transformer is widely used in the following fields:
Consumer Electronics: 150–200W laptop adapters, 24V/8A high-power fast-charging supplies, portable power stations (200W class), balancing efficiency, power density, and cost.
Industrial Control: High-power PLC module power supplies, servo drive main power supplies, auxiliary power supplies for industrial frequency converters, meeting the requirements for wide-temperature (-40℃~+200℃) operation and high insulation in industrial environments.
LED Commercial Lighting: 100–200W LED industrial and mining lights, high-mast streetlights, and shopping mall canopy light driver power supplies, supporting a high power factor (PF≥0.98) and low harmonic distortion (THD≤5%), in compliance with energy efficiency standards.
Medical Electronics: Main power supplies for medium-sized medical equipment (e.g., desktop ultrasound systems, electrocardiographs, blood analyzers), meeting medical-grade isolation withstand voltage and low leakage current requirements.
Automotive/Energy Storage Electronics: 200W automotive inverters, RV power supply modules, and main power supplies for energy storage battery management systems (BMS), suitable for the demanding automotive environment characterized by vibration, wide temperature ranges, and voltage fluctuations.
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