Integrated circuit and power supply device

1. An integrated circuit for a power supply circuit that includes a transistor and generates an output voltage of a target level, the integrated circuit being configured to switch the transistor, the integrated circuit comprising:

a first terminal configured to receive a voltage according to the output voltage;

a signal detection circuit configured to detect, through the first terminal, a setting signal received from an external circuit that operates based on the output voltage; and

a driver circuit configured to drive the transistor in response to the setting signal detected by the signal detection circuit, wherein

the driver circuit is configured to operate in an operation mode,

the setting signal has a pulse width that varies with the operation mode of the driver circuit, and

the signal detection circuit detects the setting signal based on the pulse width of the setting signal.

2. The integrated circuit according to claim 1 , wherein

the operation mode includes a first mode and a second mode, and

the driver circuit

operates in the first mode for continuously switching the transistor, in response to the pulse width of the setting signal being a first time period, and

operates in the second mode for intermittently switching the transistor, in response to the pulse width of the setting signal being a second time period.

3. The integrated circuit according to claim 2 , wherein

the operation mode further includes a third mode, and

the driver circuit operates in the third mode for stopping switching the transistor, in response to the pulse width of the setting signal being a third time period.

4. The integrated circuit according to claim 2 , wherein

the power supply circuit further includes a switch configured to change the voltage at the first terminal in response to the setting signal,

the first terminal is coupled to the switch, and

the signal detection circuit detects the setting signal based on a change in the voltage at the first terminal in a time period of the pulse width.

5. The integrated circuit according to claim 4 , wherein

the switch changes the voltage at the first terminal such that the voltage at the first terminal is a ground voltage during the time period of the pulse width.

6. The integrated circuit according to claim 5 , wherein

the signal detection circuit includes:

a determination circuit configured to determine whether the voltage at the first terminal is the ground voltage, and

a detection circuit configured to detect the setting signal, according to a time period during which the voltage at the first terminal is the ground voltage; and

the driver circuit

stops switching the transistor in response to the determination circuit determining that the voltage at the first terminal is the ground voltage, and

operates in the operation mode according to a result of detection of the detection circuit, in response to the determination circuit determining that the voltage at the first terminal is not the ground voltage.

7. The integrated circuit according to claim 6 , wherein

the detection circuit detects a first state, in response to the time period during which the voltage at the first terminal is the ground voltage being longer than a predefined time period, and

the driver circuit operates in the first mode, in response to the determination circuit determining that the voltage at the first terminal is not the ground voltage, after the detection circuit detects the first state.

8. The integrated circuit according to claim 1 , wherein

the power supply circuit further includes:

a rectifier circuit that rectifies an alternating-current (AC) voltage in the power supply circuit, and

a capacitor external to the integrated circuit; and

the integrated circuit further includes:

a second terminal configured to receive a rectified voltage from the rectifier circuit, and

a start-up circuit configured to charge the capacitor to generate a power supply voltage of the integrated circuit, based on the rectified voltage received at the second terminal.

9. A power supply device comprising:

a power supply circuit including a transistor;

a first integrated circuit configured to switch the transistor of the power supply circuit such that the power supply circuit generates an output voltage of a target level; and

a second integrated circuit configured to operate based on the output voltage, wherein

the second integrated circuit includes a setting-signal output circuit configured to output a setting signal to the first integrated circuit; and

the first integrated circuit includes:

a first terminal configured to receive a feedback voltage according to the output voltage,

a signal detection circuit configured to detect, through the first terminal, the setting signal outputted from the second integrated circuit, and

a driver circuit configured to drive the transistor in response to the setting signal detected by the signal detection circuit.