A power conversion system according to the present disclosure includes a first circuit, a second circuit, and a third circuit. A first internal terminal, a second internal terminal, and a third internal terminal are electrically connected to the same connection unit. The third circuit provides an output voltage across a secondary winding of a transformer via a switching element and the transformer. The secondary winding is electrically connected to the third internal terminal. The output voltage has a waveform including a rising range in which the output voltage changes from a first potential to a second potential, a falling range in which the output voltage changes from the second potential to the first potential, and a flat range in which the output voltage is maintained at either the first potential or the second potential.