Power supply circuit, and method for controlling the same

1. A power supply circuit, comprising:

a plurality of voltage sources;

a switch circuit that switches between a state in which the plurality of voltage sources are connected in series and a state in which the plurality of voltage sources are connected in parallel; and

a voltage control circuit that boosts an input voltage,

wherein the switch circuit connects the plurality of voltage sources in series, supplies an output of the plurality of serially connected voltage sources to an output node of the voltage control circuit, thereafter connects the plurality of voltage sources in parallel, and supplies outputs of the plurality of parallel-connected voltage sources to the voltage control circuit, and

the voltage control circuit boosts voltages of the plurality of parallel-connected voltage sources.

2. The power supply circuit according to claim 1 , wherein

the switch circuit connects the plurality of voltage sources in series and charges a capacitor, connected to an output node of the voltage control circuit, by using the output of the plurality of serially connected voltage sources, and

the switch circuit connects the plurality of voltage sources in parallel after a voltage of the output node of the voltage control circuit becomes equal to or greater than a predetermined voltage, and supplies the outputs of the plurality of parallel-connected voltage sources to the voltage control circuit.

3. The power supply circuit according to claim 1 , further comprising a booster circuit that boosts a voltage supplied from at least one of the plurality of voltage sources,

wherein the switch circuit uses the voltage boosted by the booster circuit as a power supply.

4. The power supply circuit according to claim 3 , wherein

the booster circuit is configured with a charge pump circuit,

the voltage control circuit is configured with a switching regulator, and

a frequency of an oscillator circuit provided in the charge pump circuit is lower than a frequency of an oscillator circuit provided in the switching regulator.

5. The power supply circuit according to claim 1 , further comprising a voltage monitor circuit that monitors a voltage of an output node of the voltage control circuit,

wherein the switch circuit connects the plurality of voltage sources in series when the voltage of the output node is smaller than a predetermined voltage, and

the switch circuit connects the plurality of voltage sources in parallel when the voltage of the output node is equal to or greater than the predetermined voltage.

6. The power supply circuit according to claim 5 , wherein the voltage control circuit starts boosting the voltages of the plurality of voltage sources, which are supplied through the switch circuit, at a timing when the voltage of the output node becomes equal to or greater than the predetermined voltage.

7. The power supply circuit according to claim 1 , wherein, when the switch circuit connects the plurality of voltage sources in parallel, the outputs of the plurality of voltage sources are supplied simultaneously to the voltage control circuit.

8. The power supply circuit according to claim 1 , further comprising a switching circuit that, when the switch circuit connects the plurality of voltage sources in parallel, supplies the outputs of the plurality of voltage sources sequentially to the voltage control circuit.

9. The power supply circuit according to claim 8 , wherein the voltage control circuit controls a boosting ratio dependent on the voltage sources connected to the voltage control circuit.

10. The power supply circuit according to claim 8 , further comprising an input voltage monitor circuit that monitors each of the voltages of the plurality of voltage sources,

wherein the voltage control circuit controls a boosting ratio of the voltage of each of the voltage sources according to monitor results of the input voltage monitor circuit.

11. The power supply circuit according to claim 10 , wherein the voltage control circuit sets the boosting ratio thereof in such a manner that the lower the voltages of the voltage sources are, the higher the boosting ratio becomes.

12. A method for controlling a power supply circuit that includes:

a plurality of voltage sources;

a switch circuit that switches between a state in which the plurality of voltage sources are connected in series and a state in which the plurality of voltage sources are connected in parallel; and

a voltage control circuit that boosts an input voltage, the method comprising:

connecting the plurality of voltage sources in series and supplying an output of the plurality of serially connected voltage sources to an output node of the voltage control circuit; and

connecting the plurality of voltage sources in parallel and supplying outputs of the plurality of parallel-connected voltage sources to the voltage control circuit to boost voltages of the voltage sources.

13. The method for controlling a power supply circuit according to claim 12 , comprising:

connecting the plurality of voltage sources in series and charging a capacitor, connected to the output node of the voltage control circuit, by using the output of the plurality of serially connected voltage sources; and

connecting the plurality of voltage sources in parallel after a voltage of the output node of the voltage control circuit becomes equal to or greater than a predetermined voltage, and supplying the outputs of the plurality of parallel-connected voltage sources to the voltage control circuit.