I have recently cannibalized a 6 year old microwave oven. I was very surprised to find the following beast at the electrical entry of the oven:
The reason: this small 1:1 isolation transformer was powering a 900W oven, without any switching technology (everything in the circuit remains at the main 50Hz): the big internal high voltage transformer was connected to it. I have analysed the circuit and drawn the schematic:
If I'm not wrong, the blue cubic component is a capacitor, and so are the two other small blue components (as indicated in the schematic). I guess that the resistor is a bleeder, and that the tank LC circuit is tuned to resonate at 50Hz (in order to block the current in the case where the secondary is opened). I would like to know if I am missing something, and if not, if this is a well known technique to reduce the size of the transformer connected to the mains supply. Also, what is the essential reason this thing was inserted here? Galvanic isolation?