Welcome to our blog series on planar transformers! Join us as we explore the fascinating world of this exciting technology, starting with Part I and the basics: What is a transformer? We will also discuss the advantages that the innovative design of planar transformers offers over traditional transformers. Part II will follow shortly, and we can already reveal this much: it will be about the amazing applications of printed circuit boards with planar transformers.
What is a transformer
A transformer (or transformer for short) is an essential component in electrical engineering that transforms alternating voltage and alternating current from one voltage level to another. It works on the principle of electromagnetic induction and is used to efficiently transmit electrical energy or to adjust the voltage to the needs of consumers.
Structure and function of a transformer
Core
The transformer usually consists of an iron core that bundles the magnetic field lines. This increases the efficiency of energy transfer.
primary winding
This is the coil connected to the input voltage (e.g., an AC voltage source). When alternating current flows through this coil, an alternating magnetic field is generated.
secondary winding
This coil is magnetically coupled but electrically isolated from the primary winding. The alternating magnetic field of the iron core induces an output voltage in this coil.
- When alternating current flows through the primary winding, it generates an alternating magnetic field in the core.
- This magnetic field penetrates the secondary winding and induces a voltage there in accordance with Faraday's law of induction.
- The voltage ratio between the primary and secondary windings depends on the number of windings.
Types of transformers
Increase voltage (high voltage transformer)
- The secondary winding has more turns than the primary winding
- The output voltage is greater than the input voltage.
Reduce voltage (low voltage transformer)
- The secondary winding has fewer turns than the primary winding
- The output voltage is lower than the input voltage.
The planar transformer
A planar transformer (planar transformer) is a low-voltage transformer that transmits energy contactlessly via inductive coupling. It uses flat conductor tracks on multilayer printed circuit boards (PCBs) instead of conventional wire windings.
This design enables a compact form, ideal for applications with high frequencies and limited space, such as in switching power supplies. Manual winding processes are eliminated as the windings are integrated directly into the PCB, which shortens production time and reduces susceptibility to errors.
Planar transformers are available both as individual components and integrated into extensive PCB layouts.
How a planar transformer works
Windings in the printed circuit board
- The primary and secondary windings are formed by copper conductor tracks on the layers of the printed circuit board. A high winding density is achieved through clever design (e.g., parallel layers and through-plating).
- The number of windings is determined by the number of loops on the circuit board.
Magnetic core
- The transformer requires a magnetic core to concentrate the magnetic field lines and maximize efficiency.
- Typically, a ferrite core is used, which is mounted on the circuit board as a molded part.
High frequency operation
- Planar transformers usually operate at high switching frequencies (e.g., 100 kHz to several MHz), as the magnetic core and flat windings are not ideally suited for low frequencies.
- High-frequency operation can significantly reduce the size of the transformer, as smaller cores and shorter windings are required.
Induction principle
- Just as with classic transformers, an alternating current in the primary winding is transferred to the secondary winding by an alternating magnetic field in the core.
- As with conventional transformers, the output voltage depends on the turns ratio.
Special feature of planar transformers
The planar transformer is designed and manufactured in the unpopulated PCB so that all conductor track windings are already integrated. As part of the process chain, production takes place without the magnetic core, which must then be subsequently implemented by the customer. This approach enables an optimized production line and offers the customer flexibility in selecting the appropriate core. The design of the core (e.g. E-core, U-core or toroidal core) is specified depending on the application.
| FEATURES | CLASSIC TRANSFORMER | PLANAR TRANSFORMER |
|---|---|---|
|
Construction method |
Manual wire winding around a core |
Flat copper tracks as an integrated layout part in a multilayer printed circuit board |
|
Size and weight |
Relatively large and high |
Compact and flat - weight can be reduced |
|
Heat dissipation |
Restricted by design |
Optimum dissipation via the circuit board, extending the service life of the components |
|
Energy efficiency |
Higher losses due to windings |
Precise geometry, lower losses |
|
Production costs |
Manual winding - time-consuming |
Automated production, susceptibility to errors is reduced |
Questions?
Do you have questions about planar transformers or need support with the layout and development process?
Please feel free to contact the experienced experts at our Technical Support department.
