Charging circuit

A charging circuit configured to receive electric power from a solar battery, and to charge a secondary battery, the charging circuit comprising:

• a DC/DC converter comprising a switching transistor, an inductor element, a rectifier element, and an output capacitor;
• a charging current detection unit configured to generate a detection signal that corresponds to a charging current supplied from the DC/DC converter to the secondary battery;
• a control circuit configured to generate a reference voltage that corresponds to the detection signal;
• a driving unit configured to generate a pulse signal having a duty ratio that is adjusted such that the voltage output from the solar battery matches the reference voltage, and to perform switching of the switching transistor according to the pulse signal;
• a first transistor arranged in parallel with the switching transistor;
• an oscillator configured to output a clock signal having a predetermined frequency;
• a driver configured to drive the first transistor according to the clock signal;
• a diode arranged such that its anode is connected to the first transistor;
• and
• a second output capacitor connected to a cathode of the diode,
• wherein a voltage that develops at the second output capacitor is used as a power supply voltage of the charging circuit.

An electronic device comprising:

• a solar battery;
• a secondary battery;
• and
• a charging circuit configured to receive a voltage output from the solar battery, and to charge the secondary battery,
• wherein the charging circuit comprises:
• a DC/DC converter comprising a switching transistor, an inductor element, a rectifier element, and an output capacitor;
• a charging current detection unit configured to generate a detection signal that corresponds to a charging current supplied from the DC/DC converter to the secondary battery;
• a control circuit configured to generate a reference voltage that corresponds to the detection signal;
• and
• a driving unit configured to generate a pulse signal having a duty ratio that is adjusted such that the voltage output from the solar battery matches the reference voltage, and to perform switching of the switching transistor according to the pulse signal, wherein the control circuit is configured to alternately repeat a search period in which the reference voltage is swept, and a fixed period in which the reference voltage that was detected in the search period as the voltage at which the
• charging current reaches its maximum value is fixedly output.