Editing Electric power conversion (section)

==Why use transformers in power converters==
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Transformers are used in power converters to incorporate electrical isolation and voltage step-down or step up.

The secondary circuit is floating, when you touch the secondary circuit, you merely drag its potential to your body's potential or the earth's potential. There will be no current flowing through your body. That's why you can use your cellphone safely when it is being charged, even if your cellphone has a metal shell and is connected to the secondary circuit.

Operating at high frequency and supplying low power, power converters have much smaller transformers compared with those of fundamental-frequency, high-power applications.

The current in the primary winding of a transformer help to sets up the mutual flux in accordance with Ampere's law and balances the demagnetizing effect of the load current in the secondary winding.

'''Flyback converter's transformer works differently, like an inductor.''' In each cycle, the flyback converter's transformer first gets charged and then releases its energy to the load. Accordingly, the flyback converter's transformer air gap has two functions. It not only determines inductance but also stores energy. For the flyback converter, the transformer gap can have the function of energy transmission through cycles of charging and discharging.
:<math>W_{e}=\frac{1}{2}BH=\frac{1}{2} \frac{B^2}{\mu}</math>

The core's relative permeability <math>\mu_r</math> can be > 1,000, even > 10,000. While the air gap features much lower permeability, accordingly it has higher energy density.