This circuit is one of the ways to create a floating power supply, to drive the upper two MOSFETs of an H-Bridge (see my last circuit). Notice the ground not being connected to the secondary winding of the transformer, which is referenced to the Source of the power MOSFET.
Ps: wait for the blue channel to set before trying to toggle the switch.
Edit: the push-pull stage is not referenced to ground, but to the Source of the mosfet.
