Thermal Design

Managing Heat Is Essential to Transformer Reliability

A transformer can meet its electrical specifications and still fail in the field if thermal performance is not properly controlled.

For high-frequency transformers, thermal design begins with understanding where the heat is generated.

The major sources are:

Core Loss + Winding Loss + Additional AC Losses

Core Loss

Core loss increases with operating frequency and magnetic flux.

The actual loss depends on:

• Core material
• Frequency
• Flux density
• Temperature
• Waveform

Therefore, core selection and operating flux density must be considered together.

Copper Loss

Winding losses include both DC and AC components.

DC Copper Loss

Determined primarily by:

I²R

AC Winding Loss

At higher frequencies, skin effect and proximity effect can increase effective winding resistance.

This can become significant in compact, high-power-density designs.

Temperature Rise

Transformer temperature rise is influenced by:

• Core loss
• Winding loss
• Ambient temperature
• Surface area
• Enclosure
• PCB environment
• Airflow
• Mounting configuration

A transformer should therefore be evaluated under conditions representative of its intended application.

Thermal Optimization

Depending on the application, thermal performance can be improved through:

• Lower-loss core material
• Optimized flux density
• Improved conductor selection
• Better winding arrangement
• Reduced AC winding loss
• Larger magnetic structure
• Improved heat transfer
• Encapsulation or thermal interface optimization

The objective is not simply to reduce temperature.

It is to achieve an appropriate balance between:

Efficiency + Size + Cost + Reliability

Application-Based Thermal Design

A transformer mounted inside a sealed enclosure will have very different thermal conditions from one operating in a forced-air power supply.

For this reason, HY MFG evaluates the intended operating environment when developing custom magnetic components.

Transformer running too hot?

Send us your existing specifications and operating conditions for engineering review.

Request Engineering Review