High-Frequency Switching Transformers — EE, EFD, EEL and ETD Ferrite Cores

High-frequency switching transformers are the magnetic heart of switched-mode power supplies (SMPS), converting and isolating energy at switching frequencies from roughly 20 kHz to 1 MHz. Unlike bulky 50/60 Hz mains transformers, they use low-loss ferrite cores — typically in EE, EFD, EEL and ETD shapes — that keep core loss and physical size small at elevated frequencies while transferring energy efficiently. Common core sizes such as EE10, EE19, EE28 and EEL22 span the power spectrum from a few watts to several hundred watts. ADD Components is a professional electronic components distributor supplying high-frequency switching transformers, gate-drive transformers and pulse transformers from TDK, Wurth Elektronik, Coilcraft and Pulse Electronics for SMPS, DC-DC converter and LED driver designs. This guide reviews the principal core types, key selection parameters and representative part numbers for teams buying high-frequency transformers online.

Product Types / Variants

EE Ferrite Core Transformers

The EE core is the most widely used shape in switching power supplies, with a simple square-centre-leg construction that is easy to wind and low in cost. EE cores appear across the full power range, from tiny EE10 and EE13 parts used in low-power bias supplies and gate drivers to EE19, EE25 and EE28 designs rated for tens of watts in flyback and forward converters. ADD Components sources EE-core switching transformers for offline adapters, auxiliary supplies and PoE applications, with Wurth's WE-FLEX and Coilcraft's flyback families among the most requested.

EFD Ferrite Core Transformers

EFD (economical flat design) cores are a low-profile variant of the EE core with a flattened cross-section that reduces overall height for slim-line equipment. They deliver good power handling in a compact package and are a common choice for DC-DC converters, battery chargers and flat-panel power stages where board height is constrained. EFD transformers pair well with low-profile SMT assembly and are supplied in both through-hole and surface-mount configurations.

EEL Ferrite Core Transformers

EEL cores are elongated EE-style cores with a longer winding window that accommodates more turns or larger wire, making them well suited to higher-power flyback and forward transformers. The EEL22 size, for example, offers a generous winding area for low-frequency switching designs that need higher inductance. These transformers are frequently specified in LED drivers, industrial auxiliary supplies and multi-output converters where creepage and clearance requirements are demanding.

ETD Ferrite Core Transformers

ETD (economical transformer design) cores feature a round centre leg that reduces mean turn length and winding resistance while providing good thermal dissipation through the exposed winding. They are a staple of higher-power SMPS and DC-DC converters, from a few tens of watts to several hundred watts, where low copper loss and efficient heat transfer matter. ETD transformers are widely used in offline power supplies, telecom converters and industrial power stages.

Gate-Drive and Pulse Transformers

Gate-drive and pulse transformers isolate the control circuit from the switching devices, transferring drive pulses to MOSFET and IGBT gates while providing high-voltage isolation. They typically operate at 100 kHz to 1 MHz with small volt-microsecond products and low leakage inductance. Coilcraft's DA series, Wurth's WE-AGDT series and Pulse's PH series are leading families ADD Components supplies for half-bridge, full-bridge and resonant converter designs.

Key Selection Parameters

• Switching Frequency: Match the core material and losses to the operating range (20 kHz–1 MHz); low-loss ferrite is essential above a few hundred kilohertz.

• Core Shape and Size: EE, EFD, EEL or ETD — selected for power level, height limit and winding window (e.g., EE10, EE19, EE28, EEL22).

• Turns Ratio and Outputs: Primary-to-secondary ratio and the number of secondary windings determine output voltages and cross-regulation.

• Power Rating: Confirm the continuous power in watts against your output requirement and derating under high ambient temperature.

• Input Voltage Range: Offline designs (85–265 VAC) versus DC-input converters (e.g., 36–72 V) drive different insulation and winding requirements.

• Isolation and Creepage: Verify withstand voltage (often 3–4 kV), creepage and clearance to meet safety standards such as IEC 62368-1.

• Leakage Inductance: Lower leakage inductance improves efficiency and reduces voltage spikes on the primary switch.

• Package: Through-hole versus surface-mount; confirm footprint and height for your PCB and assembly process.

Representative Transformers We Source

Send Us Your Transformer Requirements

ADD Components is a Hong Kong-based electronic components distributor supplying high-frequency switching transformers to OEM, EMS and contract manufacturing customers worldwide. We source EE, EFD, EEL and ETD ferrite-core transformers together with gate-drive and pulse transformers from TDK, Wurth Elektronik, Coilcraft and Pulse Electronics, covering SMPS, DC-DC converter and LED driver applications from a few watts to several hundred watts. Every transformer ships with factory traceability, date-code verification and anti-counterfeit screening.

Send your part numbers, target pricing or full bill of materials to Info@addcomponents.hk for a same-day quotation. We support spot buys, blanket orders and transformer wholesale programs, and we can recommend pin-compatible alternatives to consolidate your BOM and shorten lead times.

Email: Info@addcomponents.hk | Tel: +852 5334 3091 | WhatsApp: +852 5334 3091

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