The power transformer is selected depending on the requirements for itself and for the power supply as a whole. Such transformers differ from each other not only in power, but also in design, which determines their additional properties.
Instructions
Step 1
Decide at what frequency the transformer should operate. If it is connected directly to the mains, use a core of steel plates covered with an insulating layer in the transformer - at the mains frequency (50 Hz) this will be sufficient to prevent eddy currents. In a pulsed power supply, where an inverter is located between the network and the transformer, preference should be given to a ferrite core specially designed for operation at an increased frequency (tens of kilohertz). It should be borne in mind that the ferrite core, having a lower magnetic permeability compared to steel, will not be able to operate at industrial frequency. This will be equivalent to connecting the transformer to the network with the core removed, and it will inevitably burn out.
Step 2
The intensity of the stray field depends on the layout of the transformer. Cores in the shape of the letters O or W allow for quick disassembly and assembly, but components that are sensitive to the magnetic field cannot be placed next to such a transformer. Toroidal transformers emit less, but do not lend themselves to fast rewinding, moreover, they are smaller. They cannot be secured with closed rings, as they are equivalent to a short-circuited turn. If the device has a traditional layout, the windings are located separately, the capacitive coupling between them will significantly decrease. Finally, the material of the frame plays a significant role. Cardboard is easier to ignite, but harder to melt, and plastic is the other way around. If the product, which includes the transformer, is supposed to be operated around the clock, a special thermal fuse must be used. It differs from a conventional fuse in that it works not only when the current is exceeded, but also when the transformer is too hot.
Step 3
Any transformer will emit less radiation when shielding is used. When choosing a screen, be sure to take into account which field the nodes located around are sensitive to - magnetic or electric. When shielding toroidal transformers, also do not create short-circuited turns.
Step 4
Calculate the total power consumed from all secondary windings. To do this, multiply the current consumed from the winding by the voltage it develops. Add the calculation results for all secondary windings. Multiply the sum by a safety factor of one and a half to two. For a product designed for 24/7 use, use an even higher factor.
