* Product Parameters Operating frequency:10kHz-500KHz Operating temperature:-40℃ to +125℃ Storage temperature:-25℃ to +85℃ Storage humidity:30 to 95%
* Features
ER28 is a medium-to-low power high-frequency transformer core with a cylindrical center column design, excellent heat dissipation, and typical power ranging from 20W to 100W (flyback topology). It is suitable for various switching power supplies.
* Typical application areas With its moderate power capacity (typically 20W-50W) and excellent heat dissipation characteristics, the ER28 transformer is mainly used in the field of small and medium power switching power supplies, covering consumer electronics, industrial control and new energy equipment. * 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 | ER28-001 | Vertical | 28.5 | 18.0 | 11.0 | 5+5 | 3.50 | 14.00 | Φ0.6 |
| ER28-002 | Vertical | 28.5 | 18.0 | 19.0 | 5+5 | 5.00 | 17.50 | Φ0.8 |
| ER28-003 | Vertical | 28.5 | 22.0 | 22.0 | 5+5 | 5.00 | 17.80 | Φ0.8 |
| ER28-004 | Vertical | 28.5 | 23.2 | 30.0 | 5+5 | 5.00 | 17.60 | Φ0.8 |
| ER28-005 | Vertical | 28.5 | 24.2 | 37.5 | 6+6 | 5.00 | 17.60 | Φ0.8 |
| ER28-006 | Vertical | 28.5 | 24.2 | 37.5 | 5+5 | 5.00 | 17.60 | Φ0.8 |
| ER28-007 | Horizontal | 29.6 | 29.0 | 24.0 | 6+6 | 5.00 | 25.00 | Φ0.8 |
| ER28-008 | Horizontal | 29.6 | 36.5 | 25.3 | 6+6 | 5.00 | 30.00 | Φ0.8 |
| ER28-009 | Vertical | 39.5 | 27.5 | 35.0 | 9+9 | 4.00 | 20.00 | Φ0.8 |
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*The above are commonly used skeleton styles for the company.,Other styles are not included.,Inquiries are welcome. Our company can customize high-frequency transformers of various specifications according to customer requirements.
ER28 Transformer Core (External Spacing A = 28mm) is a classic size in medium-to-small power high-frequency switching power supplies. Its core performance advantages lie in the low leakage inductance and excellent thermal characteristics derived from its rounded center post design. Below is a detailed analysis of its performance parameters and features: 1. Core Physical Parameters ER28 cores are typically made from PC40 (general-purpose) or PC95 (low-loss) ferrite materials. Its key geometric parameters are as follows (note: slight variations exist between manufacturers—refer to the actual datasheet): Parameter Name | Typical Value | Description | Effective Cross-Sectional Area (Ae) | 82.1 mm² | Determines the transformer's power handling capability. A larger value allows for higher power handling. | Window Area (Aw) | 114 mm² | Determines the gauge and number of turns of enameled wire that can be accommodated, affecting current capacity. | Magnetic Path Length (Le) | ≈ 64 mm | Affects the core's magnetic reluctance and losses. | AP Value (Ae × Aw) | ≈ 9359 mm⁴ | A comprehensive indicator of the core's power handling capability. |
2. Power Range & Topology Suitability The ER28 belongs to the medium-to-small power core category, with a very wide applicable power range, primarily depending on the specific circuit topology:
Flyback Converter: This is the most common application scenario for the ER28. In flyback topologies, it typically supports power outputs from 20W to 50W, with some optimized designs supporting up to approximately 100W with improved heat dissipation.
Forward Converter: Supports power around 50W to 100W.
Resonant Converter (LLC): Benefiting from its low leakage inductance, the ER28 performs excellently in LLC resonant topologies, supporting power levels up to 300W, with operating frequencies also potentially reaching several hundred kHz.
Note: The actual power rating is also related to switching frequency, heat dissipation conditions, and insulation class. In enclosed spaces or high-temperature environments, power needs to be appropriately derated. 3. Summary of Performance Characteristics
Excellent Thermal Performance: The ER-type core's base is typically soldered directly to the PCB, allowing heat to be conducted directly through the pins and base to the PCB for dissipation. Its thermal performance is superior to similarly sized vertically mounted cores.
Low Leakage Inductance: The cylindrical center post design allows coils to be wound more tightly and uniformly, effectively reducing the transformer's leakage inductance. Low leakage inductance is crucial for improving flyback power supply efficiency and reducing losses in LLC resonant topologies.
Good Winding Processability: The smooth surface of the cylindrical center post, free of sharp edges, facilitates automated winding and results in relatively low coil distributed capacitance.
4. Design and Selection Considerations
Air Gap Adjustment: In flyback topologies, an air gap is usually required to be ground into the center post of the core. This gap prevents magnetic saturation but reduces effective permeability. Precise calculation of the air gap length is necessary to achieve the correct primary inductance.
Safety Standards: If used for AC/DC conversion, safety standards must be met (e.g., primary-to-secondary withstand voltage must exceed 3000V AC). The bobbin and barrier design must comply with safety distance standards.
Bobbin Selection: ER28 bobbins come in horizontal and vertical orientations. Horizontal mounting offers better heat dissipation, while vertical mounting occupies less board area. The choice depends on PCB space and thermal requirements.
ER28 is a transformer core widely used in medium-to-small power high-frequency switching power supplies. Its core characteristics are primarily reflected in three aspects: structural design, electrical performance, and application scenarios. 1. Structural Design Features The ER28 core adopts the classic ER (Extended Round) series structure, with its most notable feature being the cylindrical center post. This design offers the following advantages compared to traditional square center posts (e.g., EE-type):
Excellent Winding Processability: The smooth, rounded surface of the cylinder is free of sharp edges, making it easy to wind coils. It is particularly well-suited for automated winding equipment, effectively improving production efficiency.
Superior Thermal Performance: The ER28 is typically mounted horizontally, with its base in close contact with the PCB. This allows heat to be directly conducted through the pins and base to the PCB for dissipation, resulting in better temperature rise control compared to vertically mounted cores.
2. Electrical Performance Features
Moderate Power Density: The ER28 belongs to the medium-to-small power core category, with a typical power range of 20W to 100W (depending on the topology). It is commonly used for 20-50W in flyback topologies and can support up to around 100W in forward or push-pull topologies.
Good High-Frequency Characteristics: It uses high-permeability ferrite materials such as PC40 or PC95. The typical operating frequency range is 20kHz to 300kHz (some resonant topologies can reach 500kHz), with relatively low core losses.
Low Leakage Inductance: Benefiting from the cylindrical center post and optimized bobbin design, the coil distribution is uniform, resulting in relatively low leakage inductance. This is crucial for improving power supply efficiency and reducing electromagnetic interference (EMI).
3. Application Scenario Features Leveraging its moderate power handling and excellent thermal performance, the ER28 transformer is widely used in the following fields:
Industrial Power Modules: Communication power supplies, programmable switch power supplies, auxiliary power for inverters.
Consumer Electronics: LED driver power supplies, chargers, adapters.
New Energy Equipment: PV micro-inverters, DC-DC modules for energy storage systems.
ER28 Transformer Applications Leveraging its moderate power capacity (typically 20W-50W) and excellent thermal characteristics, the ER28 transformer is primarily used in medium-to-small power switching power supplies, covering consumer electronics, industrial control, and new energy equipment. Core Application Scenarios
Switching Power Supply Modules: Most commonly used in Flyback topologies, suitable for 24W-50W isolated power supply designs. Widely applied in communication power supplies, industrial power modules, and various adapters.
New Energy & Automotive Equipment: Used as auxiliary power or drive transformers in photovoltaic micro-inverters, energy storage system DC-DC modules, and on-board chargers (OBC).
Consumer Electronics & Lighting: Commonly found in LED driver power supplies, control board power for smart home devices, and complex power supply designs requiring multi-winding outputs.
Key Performance Support
Power Density: The ER28 core has an effective cross-sectional area (Ae) of approximately 82 mm². Combined with its relatively large window area, it enables the handling of medium power within a compact volume.
High-Frequency Characteristics: When paired with low-loss core materials such as PC40/PC95, its typical operating frequency can reach 50kHz-300kHz, making it suitable for high-frequency switching power supply requirements.
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