A planar transformer is a high-frequency transformer manufactured using a special structure and process, which operates based on the principle of electromagnetic induction, but differs in structure and materials from traditional wound transformers. The following are the main principles of planar transformers:

1. Electromagnetic induction:When an alternating voltage is applied to the primary winding of a planar transformer, alternating magnetic flux is generated in the magnetic core. This magnetic flux passes through both the primary and secondary windings, and according to Faraday's law of electromagnetic induction, an electromotive force is induced in the secondary winding. If the secondary winding is connected to the load, there will be current passing through, thereby achieving the transmission of electrical energy.

2. High frequency characteristics:Flat transformers typically use magnetic cores made of high-frequency power ferrite materials, which have lower core losses at high frequencies, making them suitable for high-frequency circuits. At the same time, the winding of the planar transformer is made up of multiple layers of printed circuit boards, which is conducive to reducing leakage inductance and distributed capacitance, and improving the efficiency of the transformer.

3. Structural advantagesThe magnetic core and winding of the planar transformer adopt a planar structure, which has the advantages of small size, light weight, and easy integration. This structure makes the planar transformer occupy less space in power equipment, which is beneficial for the miniaturization and lightweighting of power supplies.

PCB Design Guide

When designing the PCB of a planar transformer, the following guidelines should be followed:

Magnetic core selection:

Flat transformers typically use magnetic cores made of high-frequency power ferrite soft magnetic materials such as E-type, RM type, EC, ETD, and EER type.

When choosing a magnetic core, factors such as operating frequency, core loss, and winding space need to be considered.

Winding design:

The winding of the planar transformer is made up of multiple layers of printed circuit boards stacked together, and the winding or copper sheet is stacked on the high-frequency iron core of the planar transformer to form the magnetic circuit of the transformer.

The winding design needs to consider factors such as current density, skin effect, and proximity effect to ensure the efficiency and stability of the transformer.

There are "through holes" between the layers of the PCB for winding interconnection, and the number of turns between the windings is connected in series or parallel through the "through holes".

insulation design：

The PCB layers of the planar transformer need to be insulated by boards to ensure insulation isolation between windings, primary and secondary stages.

The selection of insulation materials needs to consider factors such as their withstand voltage level and insulation resistance.

Heat dissipation design:

Flat transformers generate heat during operation, therefore requiring heat dissipation design.

Heat dissipation measures such as heat sinks and fans can be used to improve the thermal dissipation capacity of transformers.

PCB stacking design:

When designing multi-layer PCBs for planar transformers, it is recommended to use a symmetrical stacking design to avoid deformation during PCB processing and assembly.

The thickness of the dielectric layer needs to meet the insulation requirements of primary and secondary winding, and the dielectric thickness of the entire stack should be uniform.

Other precautions:

In the design process, it is necessary to consider the manufacturing cost and processing cycle of PCB, and choose suitable boards and processes.

It is necessary to test and verify the performance of the transformer to ensure that it meets the design requirements.

In summary, the principle of planar transformers is based on electromagnetic induction and high-frequency characteristics, and their PCB design needs to follow guidelines such as core selection, winding design, insulation design, heat dissipation design, PCB stacking design, and other considerations. Through reasonable design and optimization, high-performance, miniaturized, and easily integrated planar transformers can be produced.