What Types of Transformers Are Used in Power Supplies?

ElecSuppliers Electronics GuideAug 12, 2026

Transformers are widely used in power supplies for voltage conversion, electrical isolation and energy transfer. The transformer type depends on the power supply topology, operating frequency, input and output voltage, power level and insulation requirements.

A transformer used in a traditional AC power supply can be very different from one used in a high-frequency switching power supply.

High Frequency Transformers

High frequency transformers are commonly used in switching power supplies.

They operate at much higher frequencies than traditional power-frequency transformers. The higher operating frequency allows the magnetic core and transformer to be made smaller for a given power level.

High frequency transformers are used in applications such as server power supplies, industrial power supplies, telecom equipment, EV chargers and other power conversion systems.

Core material and winding design are especially important because high-frequency operation can increase magnetic and winding losses.

Flyback Transformers

Flyback transformers are used in flyback power supply circuits.

Unlike a conventional transformer that mainly transfers energy directly between windings, a flyback transformer stores energy in its magnetic field before releasing it to the output.

They are commonly found in lower-power isolated power supplies, adapters, auxiliary power supplies and control circuits.

The core and air gap need to be designed according to the required stored energy and operating conditions.

Forward Transformers

Forward converters also use high-frequency transformers to provide isolation and transfer energy to the secondary side.

The transformer operates differently from a flyback transformer because energy is transferred to the output during the switching period rather than primarily being stored and released later.

Forward transformer designs are suitable for certain medium-power switching applications.

Push-Pull Transformers

Push-pull power supplies use a transformer driven alternately by two switching devices.

This topology can be used for DC-DC conversion and isolated power supplies.

Push-pull transformers are found in some industrial and automotive power conversion systems.

The winding structure needs to provide appropriate magnetic balance between the two switching paths.

Half-Bridge Transformers

Half-bridge converters are widely used in higher-power switching power supplies.

The transformer provides isolation and transfers energy from the switching stage to the output.

Half-bridge transformer designs can be used in applications such as industrial power supplies, telecommunications equipment and other high-power converters.

Full-Bridge Transformers

Full-bridge converters are commonly used when relatively high power needs to be converted efficiently.

The transformer operates with a full-bridge switching circuit that applies alternating voltage to the primary winding.

These transformers can be found in high-power industrial supplies, renewable energy equipment, EV charging systems and other power electronics.

LLC Transformer

LLC resonant converters use a high-frequency transformer together with resonant inductance and capacitance.

LLC designs are widely used when high efficiency and soft switching are important.

The transformer design is closely related to the resonant characteristics of the complete circuit.

This makes parameters such as magnetizing inductance and leakage inductance particularly important.

Toroidal Transformers

Toroidal transformers have a ring-shaped magnetic core.

They are widely used in low-frequency power supplies, audio equipment, industrial equipment and other applications where low electromagnetic radiation and compact construction are useful.

Toroidal transformers can provide good magnetic coupling and relatively low leakage fields when properly designed.

However, their size and weight can become significant at higher power levels and lower operating frequencies.

EI Transformers

EI transformers use a laminated core made from E-shaped and I-shaped steel laminations.

They are commonly used in traditional 50 Hz or 60 Hz power supplies and control transformers.

One advantage of EI transformers is that they are relatively straightforward to manufacture and are available in many standard configurations.

They remain common in industrial control equipment and conventional linear power supplies.

Isolation Transformers

Isolation transformers are designed primarily to provide electrical separation between circuits.

They can be used in power supplies where galvanic isolation is required for safety or system architecture.

The primary and secondary windings are electrically separated while energy is transferred through the magnetic field.

Isolation transformers can be designed for both low-frequency and high-frequency applications.

Why Transformer Selection Matters

The transformer affects several important characteristics of a power supply.

These include:

Output voltage

Power capacity

Efficiency

Temperature rise

Electrical isolation

EMI performance

Physical size

Reliability

A transformer that is not properly matched to the circuit can cause excessive losses, overheating, poor regulation or insulation problems.

How to Choose a Power Supply Transformer

Start with the input voltage, output voltage and required power.

Then determine the operating frequency and converter topology.

For high-frequency switching supplies, also consider core material, winding structure, leakage inductance, magnetizing inductance and insulation.

Temperature rise and physical dimensions should be checked against the actual installation conditions.

For high-power applications, it is also important to consider conductor size and thermal management because winding losses can become significant.

Custom Transformers for Power Supplies

Standard transformers may not always meet the requirements of a specific power supply.

A custom transformer can be designed around the actual circuit, including the required voltage ratio, power, frequency, dimensions and insulation.

The manufacturer can also optimize the core material, winding structure, conductor size and other parameters.

This can be useful for high-power switching supplies, EV chargers, solar inverters, energy storage systems and industrial power equipment.

Choosing a Transformer Manufacturer

When sourcing transformers for a power supply, consider the manufacturer's experience with the relevant transformer type and application.

Check its core materials, winding capabilities, insulation processes and testing equipment.

For custom transformer projects, engineering support is especially important because the transformer needs to work correctly with the complete switching circuit.

Choosing the Right Transformer

There is no single transformer type suitable for every power supply.

Flyback and forward transformers are used in certain switching topologies, while half-bridge, full-bridge and LLC transformers are more common in higher-power designs. Toroidal and EI transformers remain useful in low-frequency applications.

The best choice depends on the power supply topology, voltage, power, frequency, insulation requirements, efficiency target and available space.