Relationship between input power and output power of a boost converter and transformer circuit
Q3. An AC power transformer draws &quot;magnetizing current&quot;, which creates magnetic flux in the core, even when there is no load on the secondary. If there is an appropriate amount of capacitance on the secondary, a resonant circuit is created, and the current in this resonant circuit may contribute to the magnetizing current, thus reducing what is drawn from the power supply. The magnetizing current may be thought of as current going through an inductor parallel to an ideal transformer. Although this current, adds to Volt-Amp requirements, because it is going through an inductor, it does not directly add to power consumption. (Refer to power factor for more info). However, there is ohmic loss of power from the current due to the resistance of the coil. The Volt-amps drawn from the power supply should be lowest (at least to an approximation) when the resonant circuit is tuned to the frequency of the power supply.
In radio frequency transformers, creating such resonant circuits is quite common. Adding capacitative loads is also practiced by utility companies where savings can be found. However, for mains frequency transformers for home devices, resonant circuits for transformers are generally not worth the trouble.