Mechanism of transformer, AC voltage transformation

　・In Japanese
Prerequisite knowledge
　・Electromagnetic induction

■How a transformer works

A transformer is a device that converts the voltage of alternating current power by using the induced electromotive force of a coil. As shown in the diagram below, when a coil is wound around the iron core and an alternating current voltage is applied to the primary coil, voltage is applied to the secondary coil depending on the number of turns of the coil. A coil generates an electromotive force only when the voltage changes, but with alternating current, voltage changes occur all the time, so voltage can be generated continuously on the secondary side.

Note that with direct current, the direction of the current does not change, so an electromotive force can only be generated once in the secondary coil. However, even with direct current, if you use a transistor, you can turn the current on and off, so you can generate an electromotive force in the secondary coil (see: DC-DC converter). In a broader sense, a DC-DC converter is also considered a transformer, but it often converts alternating current voltage.



An example of the appearance of a transformer is shown below. These include pole-mounted transformers and toroidal transformers mounted on electronic circuits.

■Transformer losses

Transformer losses are broadly divided into copper loss and iron loss, and iron loss includes hysteresis loss and eddy current loss.

Hysteresis loss is proportional to the square of the voltage and inversely proportional to the frequency, so the lower the frequency, the greater the loss. Therefore, in order to obtain large amounts of power in the low frequency band, the iron core needs to be made larger, making the transformer larger.

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