Power supply circuit

According to one embodiment, a power supply circuit includes a source (10), a sink (20), and a connection unit. A first control circuit (CTR1) of the source (10) is configured to send an inquiry about the presence/absence of a power supply function to a second control circuit (CTR2) of the sink (20) using a first line, to turn on a changeover switch (SWC) and turn off a power reception notification switch (SWD) when a response indicating the presence of the power supply function is received, and to send a power supply request to the second control circuit (CTR2) using the first line, and the second control circuit (CTR2) is configured to turn on a power supply switch (SWA) and turn off a power source direction notification switch (SWB) when the power supply request is received from the first control circuit (CTRI), and to continue power supply during a first level period of a potential of the second line.