230V LLC Resonant Transformer ETD44 Power Transformer For Industrial Inverter

The ETD44 is a high frequency power transformer built on an ETD44 ferrite core, designed as the main isolation transformer in medium to high power switch mode conversion equipment. It transfers energy from the primary switching stage to the secondary output while maintaining full galvanic isolation between the input side and the load side, operating at switching frequencies where a low frequency transformer of the same power rating would be several times larger and heavier.

ETD stands for Economic Transformer Design, and the defining feature of the shape is its round centre post. This is not a cosmetic difference. A circle encloses a given cross sectional area with the shortest possible perimeter, so a winding placed around a round centre post has the shortest mean turn length of any core shape with the same effective area. Shorter turns mean less copper per turn, which means lower DC resistance and lower copper loss for the same number of turns. In a transformer that runs at full load continuously, this difference shows up directly as lower operating temperature.

The round post also matters for winding integrity. Wire wound around a square or rectangular centre post is bent sharply at four corners on every single turn, and each of those bends stresses the enamel insulation. A round post applies no concentrated bending stress at all, so the insulation layer stays intact. This is why ETD geometry is preferred where the winding uses fine wire, where many turns are required, or where the insulation between layers has to withstand a high potential difference over years of thermal cycling.

The ETD44 also offers a large winding window relative to its core size, which leaves room for multiple secondary windings, auxiliary and bias windings, safety margin tape, and Litz or copper foil construction where the secondary must carry high current. Its open shape allows heat to leave the winding rather than accumulate inside a closed magnetic structure.

The product is manufactured to order. Turns ratio, primary inductance, output voltages, number of windings, pin configuration, insulation system and creepage arrangement are all defined against the customer circuit and the safety standard the finished equipment must meet.

Note: output power, inductance, turns ratio and pin configuration are defined per application. Approval drawings and samples are issued for your confirmation before mass production.

Round centre post for the shortest mean turn length. A circular cross section gives the smallest perimeter for a given core area, so every turn uses less wire than the same turn wound on a square post. Less wire per turn means lower DC resistance, lower copper loss and a cooler transformer at continuous full load. Over the life of the equipment this appears as measurably better efficiency, not just a specification advantage on paper.

No corner stress on the winding. Wire wound on a rectangular post is bent sharply at four points on every turn, and each bend stresses the enamel coating. The round ETD post eliminates that stress entirely, which protects the insulation layer. For designs using fine wire, high turn counts, or high interlayer voltage, this is the difference between an insulation system that holds up for years and one that degrades quietly under thermal cycling.

Large winding window. The ETD44 provides generous window area relative to its core size, leaving room for multiple secondary windings, auxiliary and bias windings, safety margin tape and Litz or copper foil construction. Designs that would require a larger core in another shape often fit inside an ETD44.

Good thermal behaviour. The open ETD structure allows heat to escape from the winding surface rather than being trapped inside a fully enclosed core. Combined with the lower copper loss from the round post, this keeps the temperature rise well controlled at rated load.

Controlled leakage inductance. Winding sequence, interleaving and layer arrangement are engineered rather than left to chance. Leakage can be minimised to reduce voltage spike on the primary switch in a hard switched topology, or deliberately tuned to a target value so it serves as the resonant inductance in an LLC design, removing a separate resonant inductor from the bill of materials.

Robust insulation system. Layer insulation between primary and secondary, margin tape or triple insulated wire, and vacuum varnish impregnation support reinforced insulation requirements and resist partial discharge across the service life of the equipment.

Manufacturing ready. Rigid bobbin, defined pin pitch and through hole termination allow standard insertion and wave soldering, with no manual alignment step on the customer assembly line.

Designed around your controller. Topology, input range, output requirement and switching frequency define the design, so the transformer matches the controller you have already selected instead of forcing a circuit redesign.

• Industrial switch mode power supplies and DIN rail power supplies
• Solar inverters and energy storage power conversion systems
• Uninterruptible power supplies and industrial backup power
• Motor drives, servo drives and variable frequency drive supply sections
• Telecom and server rectifier modules
• Industrial battery charging systems and DC to DC converter modules
• Electric vehicle charging equipment power stages
• Welding equipment and industrial heating power supplies
• Industrial LED lighting power modules at higher power ratings
• Automation equipment and machine control power cabinets
• Test, measurement and laboratory power sources
• Medical equipment power supplies requiring reinforced isolation

Typical circuit positions include the main transformer in an LLC resonant converter, the power transformer in a half bridge or full bridge stage, the transformer in a forward converter, and the main transformer in a higher power flyback design where the ETD winding window allows the required number of windings to fit.

• Established in 2000, with 26 years of continuous experience in magnetic components and power solutions for industrial control and power electronics.
• A 10,000 square metre self owned factory with 8 complete production lines, which keeps capacity, process control and delivery schedule in house rather than subcontracted.
• High frequency transformer design and winding are core in house processes, supported by a 20 person R&D team and a 20 person quality control team covering incoming material and outgoing product inspection.
• Certified management system: ISO 9001 for quality and ISO 14001 for environment. Products comply with RoHS and REACH, with CE, CB, UL and cUL coverage across the product range.
• Annual export value of 42 million USD, serving North America, Northern Europe, South America and Southeast Asia, including established industrial equipment brands.
• An 11 person export team providing direct technical communication in English, so engineering questions are resolved without a trading company in between.

• Lower copper loss than an equivalent square post core. The round centre post shortens every turn, which lowers winding resistance and reduces heat generation at full load without any change to your circuit.
• Better insulation reliability. No corner bending stress means the enamel layer stays intact, which protects long term dielectric performance in equipment expected to run for years.
• More windings in the same core size. The large window accommodates multi output designs, auxiliary windings and safety margin construction that would otherwise force a larger core.
• Fewer components in resonant designs. Leakage inductance can be tuned to serve as the LLC resonant inductor, removing a separate component and the board space it occupies.
• Consistent inductance batch to batch. Controlled gapping, winding tooling and electrical testing before packing keep every unit inside the tolerance window your control loop depends on.
• Safety ready construction. Reinforced insulation options and UL recognised materials shorten the certification path for the finished equipment.
• Free electrical design service. Send the specification and we will propose core grade, gap, turns and wire construction, then confirm the design with samples.

Q1. What is your minimum order quantity?

Standard MOQ is 1,000 pieces. Smaller quantities can be arranged for sample evaluation and first article approval.

Q2. What payment methods do you accept?

We accept T/T, PayPal and Western Union.

Q3. What is the lead time?

Samples are normally 7 to 21 days depending on complexity. Mass production is normally 15 to 25 days after drawing approval and deposit, subject to quantity.

Q4. Can you design the transformer to match my controller and topology?

Yes, this is the normal case. Send us the topology, input voltage range, output voltage and current for each winding, switching frequency and the available space, and our engineers will define core grade, gap, turns ratio and wire construction, then confirm the design with samples.

Q5. Why choose an ETD core instead of an EE or PQ core?

The ETD round centre post gives the shortest mean turn length, so copper loss is lower than an EE core of comparable size, and it applies no bending stress to the wire at the corners. It also offers a large winding window for multi output designs. A PQ core gives higher power per unit of board footprint where the design is area limited, and an EE core is the economical general purpose option where neither loss nor window area is critical.

Q6. What output power can the ETD44 handle?

Typically 200 W to 800 W depending on topology, switching frequency, cooling and the temperature rise you are prepared to accept. Send us your operating conditions and we will confirm whether ETD44 is the right size or whether a larger core is required.

Q7. Can the leakage inductance be tuned for an LLC resonant design?

Yes. Leakage inductance can be minimised for hard switched topologies or set to a specified target value so it serves as the resonant inductance in an LLC converter. Tell us the target value and tolerance and we will design the winding arrangement to achieve it.

Q8. Can you supply a version with reinforced insulation for medical or IT equipment?

Yes. We can build with triple insulated wire or margin tape construction to meet reinforced insulation requirements, and design to the creepage and clearance distances required by IEC 61558 or IEC 62368. Tell us the standard and the working voltage before ordering.

Q9. Can you add auxiliary, bias and multiple secondary windings?

Yes. Multiple secondary windings, auxiliary supply windings for the controller and feedback windings can all be included. The ETD44 winding window is generally large enough to accommodate them without moving to a bigger core. Specify the voltage, current and tolerance for each winding.

Q10. Can the pin configuration and pin pitch be customised?

Yes. Pin count, pin pitch, pin assignment and overall height are defined against your existing PCB footprint, so the part can be a drop in replacement if you are second sourcing.

Q11. Can you add electrostatic shielding between primary and secondary?

Yes. A copper foil shield between the windings can be included to reduce common mode noise coupling, which helps with conducted emission compliance. Specify whether the shield should be grounded to the primary return or brought out on a separate pin.

Q12. What safety approvals and material compliance do you provide?

Manufacturing runs under ISO 9001 and ISO 14001. Products comply with RoHS and REACH, and UL recognised bobbin, wire and tape materials are used, with UL recognised construction available. Confirm the exact file reference applicable to your part number with your sales contact, and tell us the destination market if an additional local approval is required.

Q13. How is the transformer tested before shipment?

Primary inductance, turns ratio, leakage inductance, DC resistance and high potential isolation are tested on production equipment before packing. Test conditions are stated on the approval drawing so your incoming inspection measures the part under the same conditions we do.

Q14. Can you reverse engineer a transformer I am already using?

Yes. Send us a physical sample together with the circuit conditions and we will produce a matched replacement with the same footprint and electrical behaviour, then confirm it against your board with samples before mass production.

Q15. Do you have overseas warehouses or offer drop shipping?

No. All goods ship directly from our factory in Guangdong, China. We support FOB, CIF, DDU and DDP terms.