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Planar transformers

Planar transformers are compact multi-layer printed designs that are an alternative to using standard-type transformers and throttles. They are applied in limited systems of galvanic decoupling, and a special multi-structural spiral design allows to replace effectively voluminous and not always relevant induction coils.

Small sizes and significant technological possibilities contribute to intensive development of planar transformers technologies and, as a result, the wide spread of this printed circuit boards type.
— Telecommunication systems, including airborne/military and space communications
— Power sources
— Welding type equipment, as well as induction heating equipment
— Computer equipment
— Compact typical sizes.
— The possibility of embedding in the design of high-power impulse converters and increasing of power characteristics (when using winding packets).
— High rates of coupling coefficient, repeatability of properties and density of output power.
— Efficiency parameters: up to 98%.
— Rated operating voltage of the winding - over 1000 V.
The main design feature: the possibility of manufacturing planar transformers in the form of external components, single and multi-layer printed circuit boards.

— External components
Technological characteristics of external planar transformers are like the parameters of standard inductive models. They are independent elements. At the same time, the height of the external component is significantly reduced by immersing the core inside the board (the winding lays on the surface). Feature: the need for soldering pin/planar leads-out.

— Hybrid — single layer components
In these models one part of the winding is embedded in the motherboard, the other in a separate multi-layer printed circuit board directly connected to the motherboard. Feature: the holes must be provided in the main, maternal dielectric for a ferrite core.

— Planar transformers in the form of MPCB
In the production of these devices, the winding is fully embedded in MPCB. However, depending on the required parameters, the cores are connected by one of the methods of gluing or clamping. The basic material is FR4. Feature: the lack of wires and the need for obligatory soldering.
1. Gluing
— Ease of manufacturing automation.
— High degree of homogeneity of cross-sections.
— Small cut sizes in PCB and assembly height.
— Reliable core fixation system — absence of noise, tinkling.

2. Clamp
— Easy assembly process.
— The absence of any adverse manifestations of the external environment on production.
— The possibility of implementation in high-temperature equipment.
— High permeability properties — no increase in parasitic gaps.
Technology opportunities
Power, W
Maximum current, A
Core size, mm
from 17×15×6 to 40×32×12
 Typical size of planar transformators, mm
from 17×15×6 to 200×124×40
Frequency range, kHz
Dielectric strength, V
Weight, g