What Is a High-Frequency Transformer? A Complete Guide for Power Electronics Designers

Agenda:
1. What Is a High-Frequency Transformer?
2. Where Are High-Frequency Transformers Used?
3. Typical Products (Core Series)
4. What You Must Provide Before Designing a High-Frequency Transformer
5. High-Frequency Transformer Design Checklist (How to Use It)

 

Whether you're working with an SMPS Transformer, a Flyback Transformer, or evaluating options for your next power system, this article will help you make informed decisions.

What Is a High-Frequency Transformer?

A High-Frequency Transformer operates at frequencies above 10 kHz and can reach several MHz depending on the application. Compared to traditional 50/60 Hz power transformers, high-frequency versions offer higher efficiency, smaller size, and greater power density—making them essential in modern power electronics.

Core Functions

  • Voltage and current conversion (step-up / step-down)

  • Electrical isolation for system safety

  • Improved efficiency due to reduced magnetic losses

  • Miniaturization for compact and lightweight designs

  • Typical operating frequency range: 10 kHz to 1 MHz (special cases can reach tens of MHz)

Key Advantages

  • Smaller size and lower weight

  • High power density

  • Efficiency typically between 85%–98%

  • Flexible material choices (ferrite, nanocrystalline cores)

Where Are High-Frequency Transformers Used?

High-frequency transformers serve as the “energy hub” of many electronic systems. Typical applications include:

1. Switch-Mode Power Supplies (SMPS)

  • Server power supplies

  • Industrial-grade power systems

2. New Energy Technologies

  • EV chargers

  • DC-DC converters

  • Solar PV inverters

  • Energy storage systems (ESS)

3. Industrial and Specialized Equipment

  • High-frequency induction heating systems

  • Medical isolation power supplies

  • High-frequency welding equipment

4. Consumer Electronics & Communication

  • Routers and set-top boxes

  • LED drivers

  • Telecom base station power systems

5. Other Applications

  • UPS systems

  • X-ray equipment

  • Ignition coils

  • High-voltage power supplies

Typical Products (Core Series)

Below is a list of common transformer core series used in High-Frequency Transformer designs:

EL, EE Series  EL / EE-5.0, 8.3, 13, 16, 19, 22, 25, 28, 30, 33, 35, 40, 42, 50, 55

ER / ERL Series  ERL-28, 35, 39, 42, 49

ETD Series  ETD-29, 34, 39, 44, 49, 59

EFD Series  EFD-15, 20, 25, 30

RM Series  RM-4, 5, 6, 8, 10, 12, 14

POT Series  POT-22/13, 26/16, 30/19, 36/22

EF Series  EF-13, 16, 20, 25

PQ (PO) Series  PQ-20/20, 26/20, 32/30, 35/35, 40/40

These core types support a wide range of SMPS Transformer and Flyback Transformer designs depending on efficiency, isolation, and size requirements.

What You Must Provide Before Designing a High-Frequency Transformer

A High-Frequency Transformer is a highly customized component. Without accurate electrical and mechanical specifications, it is impossible to design proper winding structures, select suitable cores, or ensure safety compliance.

Below is the essential pre-design checklist.

1. Electrical Parameters (Most Critical)

Input Requirements

  • Input voltage range (e.g., 380–420 VDC)

  • Input current (RMS / Peak)

Output Requirements

  • Output voltage (e.g., 60 V or 40 kV peak)

  • Output current

  • Output power (rated / peak / average)

Other Key Data

  • Turns ratio (e.g., 24 V → 40 kV = 1667:1)

  • Target switching frequency (e.g., 250 kHz)

  • Topology (Flyback, LLC, Forward, etc.)

2. Operating Environment

  • Operating temperature (e.g., -40°C to 125°C)

  • Cooling method (natural convection / forced air)

  • Temperature rise limits (typically ≤ 80 K)

  • Insulation requirements (reinforced insulation, creepage ≥ 8 mm for HV)

3. Mechanical Constraints & Manufacturing Requirements

  • Specified core material or model

  • Bobbin dimensions (or “no preference”)

  • Winding configuration (dual primary, tapped winding, etc.)

  • Lead length, pin pitch, and positioning

High-Frequency Transformer Design Checklist (How to Use It)

  • Always provide core parameters, winding requirements, and basic operating conditions.

  • For high-voltage applications (e.g., 10 kV) or high-power systems (above 1000 W), notify the manufacturer in advance to ensure proper insulation and winding methods.

  • For special requirements such as ultra-thin designs, high temperature, extremely high frequency, or high current demands, supplying your circuit schematic can significantly shorten development time.

  • The design requirements may vary depending on the application of the high-frequency transformer. The checklist provided is for reference only.
High-Frequency Transformer Design Requirements
CategoryParameter ItemInput Field (Example Reference)Key Notes
I. Core Electrical Parameters1. Input Voltage Range (DC/AC)□ DC ___ V ~ ___ V
□ AC ___ V ~ ___ V  		e.g., “DC 380~420V”, “AC 90~265V”; must specify input type
2. Output Voltage (Rated / Peak)Rated ____ V; Peak ____ V
e.g., “Rated 60V; Peak 40kV”; for high-voltage applications, specify peak vs. operating voltage
3. Output Current (Rated / Peak)Rated ____ A; Peak ____ Ae.g., “Rated 27.5A; Peak 20A”; match power requirements
4. Output Power (Rated / Peak / Average)

Rated ____ W; Peak ____ W; Average ____ W

e.g., “Rated 1650W; Peak 900W; Avg 450W”; specify power type
5. Target Turns Ratio(Input : Output)____ : ____              e.g., “24:40000” (24V → 40kV), derived from voltage ratio
6. Operating Frequency (Fixed / Range)□ Fixed ____ kHz □ Range ____ kHz ~ ____ kHze.g., “Range 20~500kHz”, “Fixed 250kHz”; affects core selection and loss calculation
7. Power Topology□ LLC Resonant Half-Bridge □ Flyback □ Forward □ Others: ____e.g., "LLC Resonant Half-Bridge"; determines winding layout & core gap design
8. Primary / Secondary Inductance & DCR Requirements

Pri:____ uH;Sec:____uH; 

DCR____ mΩ

e.g., “Primary 1.2mH; Secondary 240μH”
    
II. Environmental Constraints1. Operating Temperature Range____ ℃ ~ ____ ℃e.g., “-40°C~125°C”; affects insulation material & core temperature rating
2. Cooling Method□ Natural Cooling □ Forced Air Cooling □ Others: ____Defines temperature rise limits (typically ≤80K natural, ≤60K forced)
3. Insulation Class□ Basic Insulation □ Reinforced Insulation □ Double Insulatione.g., “Reinforced Insulation”; determines creepage/clearance
4. Creepage / Clearance RequirementsCreepage & Clearance: ____ mmHigh-voltage applications (e.g., 40kV) require ≥8mm
    
III. Mechanical & Manufacturing1. Bobbin Type / Size LimitBobbin model ____ ; Max outer diameter ____ mme.g., “POT040; Max OD 40mm”; specify mounting constraints
2. Core Material / SpecificationMaterial ____ ; Size ____e.g., “PC95 ferrite; OD 40mm × H 20mm”; leave blank if not specified
3. Winding ConfigurationPrimary: ____ sets (Inductance ____ μH); Secondary: ____ sets (Inductance ____ mH); Center tap: □ Yes □ Noe.g., “Primary 2 sets (22μH/37μH); Secondary 1 set (1.55mH); center tap included”
4. Lead Wire Requirements (Length / Spacing)

Lead length ____ inch/mm;

Center spacing ≤ ____ inch/mm

e.g., “Lead length 3 inch; center spacing ≤0.5 inch”
5. Insulation Material Requirements□ Polyimide □ Polyester Film □ Mica Sheet □ Others: ____e.g., “Secondary uses PTFE HV tubing”; must meet ≥150°C and ≥5kV

>200 kHz high-frequency 12V transformer

 

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 2025-12-03