DC/DC converter, power supply circuit, and semiconductor device

A DC-DC converter comprising:

• a constant-voltage generation circuit comprising a coil and a diode;
• a transistor electrically connected to the constant-voltage generation circuit, the transistor comprising a gate electrode and a back gate electrode with a semiconductor film interposed therebetween;
• an output voltage control circuit which is configured to control a ratio of an ON time to OFF time of the transistor;
• and
• a back gate control circuit configured to control a potential applied to the back gate electrode,
• wherein the transistor is configured to control a supply of current to the coil such that induced electromotive force is generated in the coil,
• wherein one of a source and a drain of the transistor is directly connected to the coil and the diode, and
• wherein the back gate control circuit comprises:
• a current detection circuit for detecting an amount of current output from the constant-voltage generation circuit;
• and
• a power-voltage conversion circuit for determining the potential applied to the back gate electrode from the amount of the current output from the constant-voltage generation circuit and an output voltage from the constant-voltage generation circuit.

A DC-DC converter comprising:

• a constant-voltage generation circuit comprising a coil and a diode;
• a transistor electrically connected to the constant-voltage generation circuit, the transistor comprising a gate electrode and a back gate electrode with a semiconductor film interposed therebetween;
• an output voltage control circuit which is configured to control a ratio of an ON time to OFF time of the transistor;
• and
• a back gate control circuit configured to control a potential applied to the back gate electrode,
• wherein the transistor is configured to control a supply of current to the coil such that induced electromotive force is generated in the coil,
• wherein one of a source and a drain of the transistor is directly connected to the coil and the diode, and
• wherein the back gate control circuit comprises:
• a current detection circuit for detecting an amount of current output from the constant-voltage generation circuit and converting the current into a voltage;
• and
• a power-voltage conversion circuit for determining the potential applied to the back gate electrode from the amount of the current output from the constant-voltage generation circuit and an output voltage from the constant-voltage generation circuit.