* Product parameters
Operating frequency:10kHz-500KHz Operating temperature:-40℃ to +125℃ Storage temperature:-25℃ to +85℃ Storage humidity:30 to 95%
* Product features The EF20 transformer is an optimal solution for medium - power, high - frequency, high - isolation, and compact designs. With a power range of 10–50W, it features high efficiency, low temperature rise, reliable safety regulations, and mature manufacturing processes. It is suitable for various electronic devices with limited space but in need of stable isolated power supplies / drives / sampling. * Typical application fields Switch - mode power supplies& Power adapters (the most core and widely used) Industrial control and automation power supplies Communications& Network equipment power supplies LED lighting drive power supplies Automotive electronics& On - board power supplies (Automotive - grade EF25) Household appliances and consumer electronics Medical& Security auxiliary power supplies (Basic insulation level) Typical circuit topology applications
* Product standards UL, RoHS, 3C, CQC * Dimensions and specifications 
Type | Structure
Tурe | Dimension（mm） | Pin Row （mm） | Row Pitch （mm） | OD Pin
（mm） | note | A | B | C | Pin | E | F | EF25-001 | Horizontal | 25.5 | 26.2 | 19.0 | 4+4 | 5.00 | 20.00 | Φ0.8 |
| EF25-002 | Horizontal | 25.5 | 26.2 | 19.0 | 5+5 | 4.00 | 20.00 | Φ0.8 |
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* The above are the commonly used bobbin styles of the company.,Other styles are not included for the time being.,Welcome to inquire. Our company can customize high - frequency transformers of various specifications according to customer requirements.
EF25 Transformer: Comprehensive Performance Analysis The EF25 is a medium-to-high-power transformer with a standard EF structure. Its 25mm leg span provides significantly larger core cross-sectional area and window area than the EF20, offering superior power handling, thermal performance, and current capability. As a mainstream model for 30W to 80W isolated power supplies, it is widely used in adapters, industrial controls, communications, LED drivers, automotive systems, and more.
I. Structure and Dimensional Performance
Leg Span (A): 25mm, a standard medium-to-high-power EF series size with a symmetrical and mechanically stable structure.
Core: EF25 / E25/13/7 ferrite core with a large effective cross-sectional area (Ae), providing high energy storage capacity.
Bobbin: Spacious winding window allows for more turns, thicker wire, and multiple output windings.
Mounting: Vertical or horizontal mounting options with standardized pins, suitable for automated winding, insertion, and wave soldering.
Mechanical & Environmental Robustness: High mechanical strength with tight core mating, offering excellent resistance to shock, vibration, and impact. Potting (e.g., epoxy) enhances moisture, dust, and salt spray resistance.
Size Efficiency: Offers a significant power upgrade over the EF20 while using less PCB area than larger cores like EFD30 or E35, making it a primary choice for 30–80W power supplies.
II. Core and Magnetic Properties1. Common Core Materials
PC40, N87, 3C90, PC44, and other low-loss power ferrites for high-frequency operation.
Frequency Range: 20kHz to 1MHz, with optimal performance between 50kHz and 500kHz.
2. Key Magnetic Parameters
Saturation Flux Density (Bs): 380–450 mT.
Curie Temperature (Tc): ≥210°C, ensuring resistance to demagnetization and saturation at high temperatures.
Large Ae supports high-power and high-flux operation points.
Adjustable air gap stabilizes inductance, suppresses saturation, and reduces temperature rise and magnetic noise.
3. Temperature Characteristics
Operating Temperature: -40°C to +125°C.
Stable core temperature coefficient, suitable for demanding environments (industrial, outdoor, automotive, communication cabinets).
III. Core Electrical Performance1. Power Range
Typical Stable Power: 30W to 80W.
Flyback Topology (Mainstream): 30W–60W.
With good cooling and appropriate frequency, can operate stably up to 80W+.
2. Operating Frequency 3. Inductance and Leakage Inductance
Customizable Inductance: Tens of µH to several mH (measured at 10kHz/100kHz).
Typical Leakage Inductance: 15–60 µH @100kHz.
Advanced winding techniques (layered, sandwich, interleaved) further reduce leakage inductance, benefiting:
Reduced voltage spikes
Improved EMI
Enhanced loop stability
Lower RCD snubber losses
4. DC Resistance (DCR)
Primary DCR: 0.08–2 Ω (dependent on wire gauge and turns).
Secondary DCR: mΩ range, capable of supporting high-current outputs (e.g., 5V/6A, 12V/4A, 24V/2A).
Large window allows use of multi-strand Litz wire, significantly reducing high-frequency skin effect losses.
5. Insulation and Safety Compliance
Standard Inter-winding Withstand Voltage: 3kV AC / 1 min.
Reinforced/Compliance Versions: Up to 4kV–5kV AC.
Adequate Creepage and Clearance distances to meet UL, VDE, IEC, CCC, and other safety standards.
Suitable for HV-LV isolation, gate-drive isolation, signal-sampling isolation, and medical auxiliary power supplies (basic insulation).
IV. Loss and Efficiency Performance1. Copper Loss (Winding Loss) Large window area allows for thicker wire, multi-strand, or parallel windings. Minimal skin effect impact at high frequencies, resulting in low DCR and controlled temperature rise. Clear advantage over EF20/EF16 for high-current outputs.
2. Core Loss (Iron Loss)
Low high-frequency loss materials; minimized hysteresis and eddy current losses with proper flux density (Bm) design.
Stable thermal performance under medium-high power and frequency, with low risk of overheating derating.
3. Conversion Efficiency
30–60W Flyback Supplies: Efficiency 91%–96%.
High light-load efficiency, suitable for devices with strict standby power requirements (adapters, gateways, PoE, industrial power supplies).
V. Thermal Performance and Temperature Rise
Large core volume, high thermal capacity, and lower thermal resistance.
Significantly lower temperature rise compared to EF12.6 / EF16 / EF20 at the same power level.
Suitable for continuous full-load operation (industrial power, communication power, LED drivers, EVSE auxiliary power). Thermal performance and reliability can be further enhanced with PCB copper pours, chassis cooling, and potting.
VI. Safety Compliance and ReliabilityReliable Insulation Structure: Sufficient inter-layer insulation, tape isolation, sleeving, and safety distances.High dielectric strength, resistant to breakdown, tracking, and aging. Wide temperature range, moisture, vibration, and shock resistant, ideal for 24/7 operation. Capable of meeting requirements for industrial, automotive, communication, and certain medical auxiliary power insulation.
VII. Manufacturing and Mass-Production Performance
Industry-standard EF25 size with a mature and extensive supply chain for cores and bobbins.
Compatible with fully automated processes: winding, lead dressing, testing, varnishing, and potting.
High production flexibility with vertical/horizontal options.
Excellent consistency, high yield, and moderate cost, suitable for high-volume, high-reliability products.
VIII. Comprehensive Performance Summary (Technical Positioning)The EF25 is a medium-to-high-power, high-frequency, high-isolation, high-efficiency, thermally robust, and compact standard EF transformer. Covering 30W–80W, it features a large window area, ample wire gauge margin, low temperature rise, high withstand voltage, and strong reliability. It is the mainstream preferred choice for: Medium-to-high-power adapters Industrial control power supplies Communication / PoE power supplies High-power LED drivers Automotive auxiliary power supplies Servo / motor drive auxiliary power supplies
Characteristics of EF25 Transformer
I. Structural and Physical Features
Standard Medium-to-High-Power EF Structure with Clear Size Positioning
A=25mm; a primary medium-to-high power specification in the EF series, offering significantly larger size and higher power capability than the EF20.
Symmetrical E-core structure ensures excellent assembly fit and high mechanical stability.
Large Winding Window with Ample Design Margin
Window area is significantly larger than EF12.6/EF16/EF20, accommodating more turns, thicker wire gauges, and multiple secondary outputs.
Suitable for complex winding schemes requiring multiple outputs, high current, or high isolation voltage.
Universal Vertical/Horizontal Mounting for Flexible Installation
Compatible with both vertical and horizontal mounting; standard pin spacing facilitates through-hole, wave soldering, and automated assembly.
Moderate PCB footprint achieves a good balance between power density and layout space.
High Mechanical Strength and Shock/Vibration Resistance
Tight fit between core and bobbin ensures structural rigidity.
Potting optional, significantly enhancing resistance to moisture, dust, salt spray, and vibration — ideal for industrial and automotive environments.
II. Core and Magnetic Characteristics
Compatible with Low-Loss High-Frequency Ferrite Materials
Common materials: PC40, N87, 3C90, PC44, offering low high-frequency losses and excellent temperature stability.
Large Effective Cross-Sectional Area (Ae) for High Energy Storage
Larger Ae enables high magnetic flux utilization, suitable for medium-to-high power, high current, and wide input voltage applications.
Resists saturation, capable of handling higher power densities.
Adjustable Air Gap for High Inductance Stability
Air gap can be tailored to precisely control inductance, preventing magnetic saturation under high current.
Reduces temperature rise, minimizes acoustic noise, and improves dynamic load stability.
Excellent Wide-Temperature Performance
Core Curie temperature Tc ≥210°C, maintaining magnetic properties at high temperatures.
Operating temperature range: -40°C to +125°C, suitable for demanding environments (industrial, outdoor, automotive, telecom cabinets).
III. Electrical Performance Features
High Power Handling Capacity (Key Advantage)
Broad High-Frequency Compatibility
Operating frequency: 20kHz to 1MHz, with optimal efficiency between 50kHz and 500kHz.
Compatible with multiple topologies: Flyback, Forward, LLC, Push-Pull, Half-Bridge.
Low and Controllable Leakage Inductance
Standard winding: leakage inductance 15–60µH @100kHz.
Can be further reduced via layered, sandwich, or interleaved winding techniques, improving EMI, reducing voltage spikes, and enhancing loop stability.
Low DCR and High Current Capability
Large window enables thick wire, multi-strand, or Litz wire use, minimizing high-frequency skin effect losses.
Secondary DCR can reach mΩ levels, supporting high-current outputs like 5V/6A, 12V/4A, 24V/2A.
High Isolation Voltage with Strong Safety Margin
Standard inter-winding withstand voltage: 3kV AC / 1min; reinforced versions available up to 4kV–5kV AC.
Ample creepage and clearance distances easily meet UL, VDE, IEC, CCC safety standards.
Suitable for HV-LV isolation, gate-drive isolation, signal sampling isolation, and basic insulation for medical auxiliary supplies.
IV. Loss and Efficiency Features
Low Copper Loss and Superior Temperature Rise Control
Low Core Loss and Stable High-Frequency Performance
Paired with low-loss ferrite materials, minimizing hysteresis and eddy current losses.
Excellent balance between efficiency and heat generation at medium-to-high frequencies and power levels.
High Conversion Efficiency
Typical flyback power supplies (30–60W) achieve 91%–96% efficiency.
High light-load efficiency, suitable for devices with stringent standby power requirements.
V. Thermal Performance and Temperature Rise
Large core volume provides high thermal capacity and low thermal resistance.
Significantly lower temperature rise compared to EF20/EF16/EF12.6 at the same power level.
Suitable for 24/7 continuous full-load operation.
Power and reliability can be further enhanced with PCB copper pours, heatsinking, and potting.
VI. Manufacturing and Mass Production Features
Industry-standard size ensures a mature and stable supply chain.
Highly compatible with automated processes: winding, testing, varnish dipping, potting.
Excellent batch-to-batch consistency, high yield, ideal for mass production.
Cost-effective, offering better value than non-standard EFD or E-series cores of similar power.
VII. Comprehensive Summary of Core Characteristics (Concise Version)The EF25 (A=25mm) is a standard EF transformer characterized by medium-to-high power, high frequency, high isolation, high efficiency, large window, strong thermal performance, and robust structure:
High Power: 30W–80W primary range.
Compact Size: High power density, saves space.
Large Window: Enables high-current, multi-output, and high-voltage designs.
Low Leakage, Low Loss, High Efficiency.
Wide Temperature Range, Vibration Resistant, Ample Safety Margin.
Mature Process: Suitable for mass-produced, high-reliability products.
EF25 Transformer Application Scenarios by Industry The EF25 is a highly versatile, medium-to-high power transformer within the EF series, known for its reliability and broad applicability. With a typical power range of 30W to 80W, it excels in applications requiring isolation, high-frequency operation, high current capability, and continuous full-load operation. It is widely used across industries including power supplies, industrial control, communications, lighting, automotive, and security. Details by industry are provided below.
I. Switching Power Supplies & Power Adapters (Primary, Highest Volume Applications)
The EF25 is the preferred core for 30W–60W adapters, balancing size, power, thermal performance, and cost.
Typical Applications:
Laptop power supplies, tablet fast chargers, built-in monitor power.
Power adapters for home appliances (printers, projectors, speakers, small appliances).
Industrial-grade compact switching power supplies, auxiliary supplies for DIN-rail power modules.
Wide-input-voltage power supplies (85–265V AC).
Topology: Primarily Flyback, also suitable for Forward and LLC half-bridge auxiliary supplies.
Key Benefits: Adequate power, low temperature rise, high efficiency, and easy compliance with safety standards.
II. Industrial Control & Automation Power Supplies
Industrial power demands 24/7 stability, wide-temperature operation, noise immunity, and reliable isolation, which aligns well with EF25 characteristics.
Typical Applications:
Auxiliary power for PLCs, industrial motherboards, DCS systems.
Isolated power for sensors, transmitters, data acquisition modules. Isolation power for RS485 / CAN / Industrial Ethernet interfaces.
Isolated driver power for relays, solenoid valves, contactors.
Internal auxiliary power for servo drives and variable frequency drives (VFDs).
Key Benefits: High insulation withstand voltage (up to 3kV–5kV AC), vibration resistant, wide operating temperature (-40°C to +125°C).
III. Communication & Networking Equipment Power Supplies
Communication equipment requires low standby power, high isolation, high stability, and long lifespan.
Typical Applications:
Built-in power for routers, switches, enterprise gateways, OLTs. Power over Ethernet (PoE) powered device (PD) modules (medium-to-high power). Low-power auxiliary supplies for optical modules, communication boards, base stations.
Isolated power for server monitoring, BMC, and management systems.
Key Benefits: Low leakage inductance (EMI-friendly), high efficiency, capable of sustained full-load operation without thermal degradation.
IV. LED Lighting Driver Power Supplies
EF25 is commonly used in medium-power isolated LED drivers for indoor and outdoor lighting.
Typical Applications:
30W–60W isolated LED drivers (panel lights, downlights, high-bay lights, floodlights). Smart lighting, dimmable power supplies, isolated control power for 0–10V / DALI.
Built-in isolated power supplies for street lights and landscape lighting.
Key Benefits: Low temperature rise, stable core (low acoustic noise), safe isolation, suitable for long-term continuous operation.
V. Automotive Electronics & On-board Power Supplies (Automotive-grade EF25)
Automotive-grade EF25 versions can be used for non-safety-critical auxiliary power in vehicles.
Typical Applications:
On-board chargers, DC-DC auxiliary power supplies.
Internal auxiliary windings in On-Board Chargers (OBC).
Isolated power for lighting control, infotainment systems, instrument clusters, cameras.
Auxiliary and isolated sampling power for Battery Management Systems (BMS).
Key Benefits: Wide-temperature operation, shock and vibration resistant, strong noise immunity, stable magnetic performance.
VI. Home Appliances & Consumer Electronics
Home appliances prioritize safety isolation, low cost, high consistency, and mass production. Typical Applications: Control board power for air conditioners, washing machines, refrigerators.
Power supplies for air purifiers, ventilation systems, humidifiers.
Power supplies for projectors, audio systems, amplifiers, smart home hubs.
Isolated power for high-power cameras, NVRs, and security devices.
Key Benefits: Ample safety margin, reliable insulation, cost-effective, suitable for high-volume production.
VII. Medical & Security Auxiliary Power Supplies (Basic Insulation Level)
With proper safety design, the EF25 can be used in:
Typical Applications:
Auxiliary and control power for medical devices (non-patient-contact applications).
Isolated power for security cameras, access control, alarms, intercom systems.
Internal isolated power for test and measurement instruments.
Key Benefits: High withstand voltage, sufficient creepage distance, low leakage inductance, low noise.
VIII. Typical Circuit Topology Applications
The EF25 is compatible with almost all medium-power, high-frequency, isolated topologies: Flyback Power Supplies (Most Common)
Forward Converters
LLC / Half-Bridge / Push-Pull Auxiliary Windings
Gate-Drive Isolation Power Supplies
Sampling / Signal Isolation Power Supplies
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