Power supply circuit, control circuit thereof, and electronic apparatus

1. A power supply circuit comprising:

a DC/DC converter comprising at least two switching elements and configured to receive an input voltage in an input line and generate an output voltage in an output line; and

a linear regulator configured to receive the output voltage of the output line of the DC/DC converter, stabilize the received output voltage to a target level, and supply the stabilized voltage to a corresponding load,

wherein the DC/DC converter is configured to switch between a switching mode to switch the switching elements such that the output voltage approaches the target level and a bypass mode to put a switching element existing on a path from the input line to the output line, of the switching elements, in a full-on state and stop switching of the other switching element,

wherein the switching mode includes a PWM (pulse width modulation) mode and a PFM (pulse frequency modulation) mode, and

wherein, when switching from the bypass mode to the switching mode, a target value of the output voltage in the switching mode starts to smoothly decrease from a value that is larger than a normal value to the normal value, allowing the output voltage to decrease to the normal value while following the target value.

2. The power supply circuit of claim 1 , wherein the DC/DC converter is a step-down type DC/DC converter comprising a switching transistor and a synchronous rectification transistor as the switching elements and, in the bypass mode, fully turns on the switching transistor and turns off the synchronous rectification transistor.

3. The power supply circuit of claim 1 , wherein the load connected to the linear regulator is a microcomputer, and

wherein the DC/DC converter selects one of the switching mode and the bypass mode based on an instruction from the microcomputer.

4. The power supply circuit of claim 1 , wherein the DC/DC converter selects the bypass mode when an electronic apparatus equipped with the power supply circuit enters a standby state.

5. The power supply circuit of claim 1 , wherein the DC/DC converter includes a current detector to detect an output current and selects one of the switching mode and the bypass mode based on an amount of the output current.

6. The power supply circuit of claim 1 , wherein the DC/DC converter stops operations other than an operation required to fix a state of the switching elements in the bypass mode.

7. The power supply circuit of claim 1 , wherein the DC/DC converter is configured to switch between a PWM (pulse width modulation) mode and a PFM (pulse frequency modulation) mode in the switching mode, and

wherein, when switching from the bypass mode to the switching mode, regardless of an amount of an output current of the DC/DC converter, the DC/DC converter selects the PWM mode temporarily and then selects one of the PWM mode and the PFM mode based on the amount of the output current.

8. An electronic apparatus comprising:

a battery;

one or more loads; and

a power supply circuit of claim 1 , wherein the power supply circuit receives a voltage of the battery and supplies power to the one or more loads.

9. An electronic apparatus comprising:

a battery;

an application processor;

a baseband processor; and

a power supply circuit configured to supply power to the application processor and the baseband processor,

wherein the power supply circuit comprises:

a DC/DC converter comprising at least two switching elements and configured to receive an input voltage of the battery in an input line and generate an output voltage in an output line;

a first linear regulator configured to receive the output voltage of the output line of the DC/DC converter, stabilize the received output voltage to a first target level, and supply the stabilized voltage to the application processor; and

a second linear regulator configured to receive the output voltage of the output line of the DC/DC converter, stabilize the received output line voltage to a second target level, and supply the stabilized voltage to the baseband processor,

wherein the DC/DC converter is configured to switch between a switching mode to switch the switching elements such that the output voltage approaches the first and second target levels and a bypass mode to put a switching element existing on a path from the input line to the output line, of the switching elements, in a full-on state and stop switching of the other switching element,

wherein the switching mode includes a PWM mode and a PFM mode, and

wherein, when switching from the bypass mode to the switching mode, a target value of the output voltage in the switching mode starts to smoothly decrease from a value that is larger than a normal value to the normal value, allowing the output voltage to decrease to the normal value while following the target value.

10. The electronic apparatus of claim 9 , wherein the DC/DC converter selects one of the switching mode and the bypass mode based on an instruction from the application processor.

11. A control circuit of a power supply circuit configured to supply power to one or more loads,

wherein the power supply circuit comprises:

a DC/DC converter comprising at least two switching elements and configured to receive an input voltage in an input line and generate an output voltage in an output line; and

a linear regulator configured to receive the output voltage of the output line of the DC/DC converter, stabilize the received output voltage to a target level, and supply the stabilized voltage to a corresponding load,

the control circuit comprising:

a controller configured to control an on/off state of the switching elements and switch between a switching mode to switch the switching elements such that the output voltage approaches the target level and a bypass mode to put a switching element existing on a path from the input line to the output line, of the switching elements, in a full-on state and stop switching of the other switching element,

wherein the switching mode includes a PWM mode and a PFM mode,

wherein, when switching from the bypass mode to the switching mode, a reference voltage indicating a target value of the DC/DC converter in the switching mode starts to smoothly decrease from a value that is larger than a normal value to the normal value, allowing the output voltage to decrease to the normal value while following the reference voltage.

12. The control circuit of claim 11 , wherein the DC/DC converter is a step-down type DC/DC converter comprising a switching transistor and a synchronous rectification transistor as the switching elements and, in the bypass mode, fully turns on the switching transistor and turns off the synchronous rectification transistor.

13. The control circuit of claim 11 , wherein the load connected to the linear regulator is a microcomputer, and

wherein the controller selects one of the switching mode and the bypass mode based on an instruction from the microcomputer.

14. The control circuit of claim 11 , wherein the controller selects the bypass mode when an electronic apparatus equipped with the power supply circuit enters a standby state.

15. The control circuit of claim 11 , further comprising a current detector to detect an output current of the DC/DC converter,

wherein the controller selects one of the switching mode and the bypass mode based on an amount of the output current.

16. The control circuit of claim 11 , wherein the controller stops operations other than an operation required to fix a state of the switching elements in the bypass mode.

17. The control circuit of claim 11 , wherein the controller further comprises a voltage source to generate the reference voltage, and

wherein, when switching from the bypass mode to the switching mode, the voltage source sets the reference voltage.

18. The control circuit of claim 11 , wherein the controller is configured to switch between a PWM mode and a PFM mode in the switching mode, and

wherein, when switching from the bypass mode to the switching mode, regardless of an amount of an output current of the DC/DC converter, the controller selects the PWM mode temporarily and then selects one of the PWM mode and the PFM mode based on the amount of the output current.

19. The control circuit of claim 11 , wherein the control circuit is integrated on a single semiconductor substrate.

20. The power supply circuit of claim 1 , wherein the value that is larger than the normal value is set close to the input voltage.