Integrated circuit having dynamic switching control and power supply circuit including the same

A power supply circuit configured to generate an output voltage from an input voltage thereof, the power supply circuit comprising:

• a transformer including a primary coil, a secondary coil, and an auxiliary coil;
• a first transistor configured to control a current flowing through the primary coil;
• and
• an integrated circuit configured to drive the first transistor and to perform control such that the output voltage reaches a target level, the target level being changeable between a first level and a second level lower than the first level, the integrated circuit including
• a determination circuit configured to determine whether driving of the first transistor is stopped, based on the output voltage,
• an oscillator circuit configured to output an oscillator signal,
• a driving signal output circuit configured to
• output a driving signal to turn on the first transistor in response to the oscillator signal, and
• output the driving signal to turn off the first transistor, in response to a voltage corresponding to a current flowing through the first transistor when the first transistor is on reaching a voltage corresponding to the output voltage, a buffer circuit configured to, after a delay of a predetermined time,
• stop the driving of the first transistor, in response to an output from the determination circuit indicating that the driving of the first transistor is to be stopped, and
• drive the first transistor, based on the driving signal, in response to the output from the determination circuit indicating that the driving of the first transistor is not to be stopped;
• and
• a control circuit configured to
• operate the buffer circuit, after the target level is changed to the first level, and
• stop an operation of the buffer circuit, in response to the determination circuit determining that the driving of the first transistor is stopped, after the target level is changed to the second level.

A power supply circuit configured to generate an output voltage from an input voltage thereof, the power supply circuit comprising:

• a transformer including a primary coil, a secondary coil, and an auxiliary coil;
• a first transistor configured to control a current flowing through the primary coil;
• and
• an integrated circuit configured to drive the first transistor and to perform control such that the output voltage reaches a target level, the target level being changeable between a first level and a second level lower than the first level, the integrated circuit including
• a first oscillator circuit configured to output a first oscillator signal having a first frequency corresponding to the output voltage,
• a second oscillator circuit configured to output a second oscillator signal having a predetermined second frequency,
• a feedback voltage generating circuit configured to generate a feedback voltage according to the output voltage,
• a driver circuit configured to
• drive the first transistor in response to the first oscillator signal, when the target level of the output voltage is the first level and the feedback voltage fluctuates in a first voltage value range, and
• drive the first transistor in response to the second oscillator signal, when the target level is the second level and the feedback voltage fluctuates in a second voltage value range, and
• a control circuit configured to stop an operation of the first oscillator circuit, after the target level is changed to the second level, wherein
• the first voltage value range and the second voltage value range overlap each other, and
• the driver circuit is further configured to drive the first transistor in response to the first oscillator, when the target level of the output voltage is the first level in both a first period in which the feedback voltage increases and a second period in which the feedback voltage decreases.

An integrated circuit for a power supply circuit configured to generate an output voltage of a target level from an input voltage thereof, the target level being changeable between a first level and a second level lower than the first level, the power supply circuit including

• a transformer including a primary coil, a secondary coil, and an auxiliary coil, and
• a first transistor configured to control a current flowing through the primary coil, the integrated circuit being configured to drive the first transistor, the integrated circuit comprising:
• a determination circuit configured to determine whether driving of the first transistor is to be stopped, based on the output voltage;
• an oscillator circuit configured to output an oscillator signal;
• a driving signal output circuit configured to
• output a driving signal to turn on the first transistor in response to the oscillator signal, and
• output the driving signal to turn off the first transistor, in response to a voltage corresponding to a current flowing through the first transistor when the first transistor is on reaching a voltage corresponding to the output voltage;
• a buffer circuit configured to, after a delay of a predetermined time,
• stop the driving of the first transistor, in response to an output from the determination circuit indicating that the driving of the first transistor is to be stopped, and
• drive the first transistor, based on the driving signal, in response to the output from the determination circuit indicating that the driving of the first transistor is not to be stopped;
• and
• a control circuit configured to
• operate the buffer circuit after the target level is changed to the first level, and
• stop an operation of the buffer circuit, in response to the determination circuit determining that the driving of the first transistor is stopped, after the target level is changed to the second level.