* Product parameters
Operating frequency:10kHz-500KHz Operating temperature:-40℃ to +125℃ Storage temperature:-25℃ to +85℃ Storage humidity:30 to 95%
* Product features In terms of the structure of the EE33 transformer,it is standardized, with low cost and easy to purchase. There are many types of bobbins, which are easy to wind and install. The window area is large, and it is convenient for safety regulations design. In terms of power, the power range is moderate, with wide applicability. The air - gap is adjustable, the design is flexible, the saturation magnetic flux is high, and the number of turns can be reduced. In terms of thermal management, the surface area is large, and the natural heat dissipation is good.
* Typical application fields
* 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 | EE33-001 | Vertical | 35.0 | 30.0 | 32.5 | 6+6 | 5.0 | 22.5 | Φ0.80 |
| EE33-002 | Vertical | 36.0 | 30.0 | 32.5 | 7+7 | 5.0 | 22.5 | Φ0.80 |
| EE33-003 | Vertical | 40.0 | 30.0 | 32.5 | 8+8 | 5.0 | 22.5 | Φ0.80 |
| EE33-004 | Vertical | 45.0 | 30.0 | 32.5 | 9+9 | 5.0 | 22.5 | Φ0.80 |
| EE33-005 | Vertical | 48.0 | 32.0 | 32.5 | 17+17 | 2.54 | 20.5 | Φ0.70 |
| EE33-006 | Vertical | 48.0 | 32.0 | 31.5 | 18+18 | 2.54 | 23.0 | Φ0.70 |
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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 consult. Our company can customize high - frequency transformers of various specifications according to customer requirements.
EE33 Transformer Electrical Performance Analysis The EE33 transformer (external span A=33mm) is a high-power, high-frequency transformer. Compared to models like the EE28 and EE30, its core's effective cross-sectional area (Ae) and window area (Aw) achieve a significant leap, reaching industrial-grade high-end standards in power handling capability, thermal stability, and interference resistance. Its core electrical performance is determined by core material selection, winding process design, topology scheme matching, and heat dissipation system configuration, making it suitable for 200–400W high-power supply scenarios. The following analysis covers core parameters, performance influencing factors, typical applications, 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) | 5mH–100mH | Determined by core AL value, turns, and air gap; tolerance ±0.5% to ±2%; high air gap adjustment precision, suitable for high-power resonant topologies. | Leakage Inductance (Lk) | 0.1%–0.6% of L | Under same process, leakage inductance is far lower than medium and small power cores, significantly reducing voltage spikes and simplifying EMI filter design. | DC Resistance (DCR) | Primary: 0.03–0.8Ω; Secondary: 0.008–0.3Ω | Extra-large window area allows for large wire diameter or multiple parallel strands, achieving industry-leading copper loss control. | Loss & Efficiency | Core Loss (Pc) | 1000–2500mW | Increases with frequency/flux density; N97 material's high-frequency loss is over 35% lower than N87, with excellent high-temperature resistance. | Copper Loss (Pcu) | 1200–3000mW | Affected by current density/winding process; Litz wire effectively suppresses skin effect above 200kHz. | Efficiency (η) | 95%–99% | Higher efficiency than EE30 at equivalent power; full-load efficiency in LLC topology can exceed 98.5%. | Safety & Insulation | Isolation Withstand Voltage | Primary-Secondary: 8–12kV AC/1min | Bobbin barrier height ≥15mm, creepage distance ≥12mm, meeting medical Class A and heavy-duty industrial equipment safety standards. | Insulation Resistance | ≥5000MΩ (500VDC) | Excellent moisture and salt spray resistance, suitable for outdoor and high-humidity industrial environments. | Thermal Performance & Endurance | Operating Frequency | 5kHz–500kHz | Saturation risk is negligible at low frequencies, high-frequency loss is controllable, covering scenarios from power frequency critical points to high-frequency switching supplies. | Output Power | 200–400W | 250W with natural convection; up to 400W with heatsink and forced air cooling. | Operating Temperature | -40℃~+250℃ | Compatible with Class C (220℃) and HC (250℃) insulation systems; full-load temperature rise ≤70℃. |
II. Key Factors Affecting Performance 1. Core Characteristics: Core Support for High-Power Handling Advantage of external span A=33mm: Effective cross-sectional area (Ae) increases by approximately 40% compared to EE30, geometrically enhancing flux handling capability, making core saturation risk under high-current conditions virtually zero. The significantly larger window area (Aw) can accommodate large-diameter windings, multi-layer insulation structures, and shielding layers simultaneously, meeting design needs for high inductance, low copper loss, and high insulation. Air Gap Design: Optimal air gap range is 0.8–3.0mm.
Forward Topology: Requires a very small and uniform air gap (0.8–1.5mm) to ensure fast core reset.
Flyback Topology: The air gap can be increased (2.0–3.0mm) to significantly boost saturation current and short-term overload capability.
LLC Resonant Topology: Requires high-precision air gap grinding to ensure high matching between magnetizing inductance and resonant parameters, reducing resonant circulating current 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 large 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 200–400W supplies, primary wire diameter is recommended at 1.2–2.5mm, secondary at 2.5–3.5mm. For high output current, the secondary uses 10–20 parallel strands of 1.2mm wire to maximize suppression of skin and proximity effects. Winding Technique: Using interleaved winding (e.g., primary-secondary-primary-secondary) plus a quadruple-layer copper foil shield can control leakage inductance to within 0.3% of the main inductance. A quadruple insulation barrier of Nomex paper + polyimide film + epoxy board + insulating adhesive between primary and secondary meets high isolation withstand voltage requirements. For high-frequency operation, use Litz wire with strand diameters of 0.25–0.35mm, reducing high-frequency copper loss by 45–55%. Insulation Design: Inter-layer insulation thickness ≥0.4mm, primary-secondary creepage distance ≥12mm, meeting safety standards like UL60601-1 (Medical Class A) 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 300–400W high-efficiency power supplies, efficiency can exceed 98.5%. The low leakage inductance of EE33 reduces resonant loss and improves system dynamic response, making it the preferred topology for server power supplies, energy storage stations, and charging pile modules.
Forward Topology: Suitable for 200–300W low-ripple power supplies, requiring an active clamp + synchronous rectifier circuit. The large Ae reduces flux density, decreasing core loss, suitable for precision industrial control and medical equipment power supplies.
Flyback Topology: Suitable for 200–250W cost-sensitive solutions. Compared to EE30, it can use fewer turns and larger wire diameter, further reducing copper loss. Short-term overload capability can reach 200% of 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 a combined cooling system of thermal grease + aluminum finned heatsink + high-power turbo fan can reduce temperature rise by 35–45℃.
Load Rate: Optimal efficiency typically occurs at 85–95% load. Under light load (<20%), optimize winding distributed capacitance to reduce standby loss to below 120mW.
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 + quadruple-layer copper foil shielding to control leakage inductance within 0.2%.
Thermal Optimization: Apply high thermal conductivity coating on the core surface and attach a large-area finned heatsink. Design an independent forced air cooling duct with wind speed ≥4m/s to improve forced convection cooling efficiency.
Parameter Matching: For LLC topology, prioritize magnetizing inductance accuracy (tolerance ±0.5%). For Forward topology, reduce the air gap and match active clamp parameters. For Flyback topology, increase the air gap to enhance saturation resistance.
Core Characteristics of EE33 Transformer The EE33 transformer (i.e., a transformer built around an EE33 core) is a classic and versatile component in the field of power electronics. Its characteristics are defined by the physical properties of the core itself, manufacturing processes, and application scenarios. Below is a detailed analysis of its characteristics from five dimensions: structural, electrical, thermal, application, and advantages/disadvantages. I. Structural Characteristics Standardization and Versatility:
EE33 is an internationally recognized standard size. Major magnetic material manufacturers (TDK, EPCOS, Ferroxcube, domestic producers, etc.) all produce it, resulting in a mature supply chain, high cost-effectiveness, and easy procurement and replacement.
Bobbin and Winding:
A wide variety of compatible plastic bobbins are available (pin type, SMD type; with barriers, without barriers), facilitating automated winding and PCB mounting.
The relatively large window area is beneficial for:
Using thicker enameled wire to reduce copper loss.
Winding multiple output windings or adding shielding layers.
More easily meeting safety insulation requirements (e.g., number of tape layers between primary and secondary sides, barrier distance).
Assembly and Air Gap:
Composed of two 'E' cores assembled together, making assembly straightforward.
Flexible air gap adjustment: The air gap can be introduced on the center leg (most common) or the side legs. Grinding the center leg or inserting gap material (e.g., insulating spacers) allows for precise control of inductance, which is crucial for the design of flyback transformers and power inductors.
II. Electrical Performance Characteristics Medium Power Range:
Typically used in switching power supplies (most common in flyback topology). Its upper power limit depends on switching frequency, heat dissipation conditions, and topology (Forward, Half-Bridge, etc., can achieve higher power).
Excellent High-Frequency Characteristics:
When high-frequency, low-loss ferrite materials like PC40, PC44 are used, it offers a wide operating frequency range, typically 50kHz ~ 250kHz, and can reach 500kHz or higher with optimization (e.g., LLC resonant topology).
High Saturation Flux Density:
Using PC40 material, the saturation flux density (B_s) at 100°C is approximately 390mT. This allows it to operate at relatively high flux densities (design values often range from 150-300mT), thereby enabling a reduction in primary turns, lowering copper loss and leakage inductance.
Leakage Inductance and Coupling:
"Sandwich winding" is often used with EE-type cores to reduce leakage inductance, and the EE33's window space facilitates this.
However, due to its magnetic path structure, the leakage inductance is typically slightly higher compared to round cores like PQ, RM. In high-efficiency or high-power-density designs, careful winding structure design is needed to control leakage inductance.
III. Thermal Performance Characteristics Good Heat Dissipation Capability:
The EE-type core has a relatively large surface area, which is conducive to dissipating core loss (iron loss) and some winding heat through natural convection or forced air cooling.
The core itself can act as a small heat sink, and the center leg in contact with the windings can help conduct heat.
Thermal Distribution:
Heat primarily originates from winding copper loss and core iron loss. Due to the EE33's large window area, the winding space is relatively ample, which helps lower current density and thus control the temperature rise from copper loss.
Typical Application Scenarios Leveraging its high-power capacity and excellent stability, the EE33 transformer is widely used in the following fields:
Consumer Electronics: 300–400W laptop adapters, 24V/15A high-power fast-charging supplies, portable power stations (400W class), balancing efficiency, power density, and cost.
Industrial Control: High-power PLC module power supplies, servo drive main power supplies, main power supplies for industrial frequency converters, and CNC machine tool power supplies, meeting the requirements for wide-temperature (-40℃~+250℃) operation and high insulation in industrial environments.
LED Commercial Lighting: 300–400W LED industrial and mining lights, high-mast streetlights, and sports venue lighting driver power supplies, supporting a high power factor (PF≥0.995) and low harmonic distortion (THD≤2%), in compliance with energy efficiency standards.
Medical Electronics: Main power supplies for large medical equipment (e.g., MRI scanners, hemodialysis machines, ventilators), meeting medical-grade isolation withstand voltage and low leakage current requirements.
Automotive/Energy Storage Electronics: 400W automotive inverters, RV power supply modules, main power supplies for energy storage battery management systems (BMS), and small charging pile modules, suitable for the demanding automotive environment characterized by vibration, wide temperature ranges, and voltage fluctuations.
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