Charging circuit and mobile terminal

1. A charging circuit, coupled between a charging interface of a mobile terminal and a battery of the same mobile terminal and configured to charge the battery of the same mobile terminal, the charging circuit comprising a first circuit, a magnetic coupling element, and a second circuit connected in series between the charging interface and the battery, wherein the mobile terminal is operable in a normal charging mode and a fast charging mode, and a charging current is larger in the fast charging mode than in the normal charging mode, wherein

the first circuit is configured to receive a first current from the charging interface and convert the first current to a second current with at least one of a magnitude and a direction changed wherein the charging interface is a universal serial bus (USB) interface and the first current is a direct current (DC);

the magnetic coupling element comprises a first coil and a second coil, the first coil is connected with the first circuit, the second coil is connected with the second circuit, and the first coil and the second coil are separated from each other to disconnect a direct current path of the charging circuit when the first circuit fails, wherein the magnetic coupling element is configured to transfer energy from the first coil to the second coil in an electromagnetic induction manner by utilizing the second current with at least one of a magnitude and a direction changed when the first circuit outputs the second current to generate a third current at the second coil;

the second circuit is configured to adjust the third current to a fourth current suitable for battery charging to charge the battery; and

the first circuit comprises a full-bridge circuit and a control circuit controlling the full-bridge circuit, and the full-bridge circuit comprises a first switch transistor, a second switch transistor, a third switch transistor, and a fourth switch transistor, wherein the first switch transistor has a first end configured to be connected with the charging interface, a second end connected with a second end of the first coil, and a control end connected with the control circuit, wherein the second switch transistor has a first end connected with the second end of the first switch transistor, a second end configured to be grounded, and a control end connected with the control circuit, wherein the third switch transistor has a first end configured to be connected with the charging interface, a second end connected with a first end of the first coil, and a control end connected with the control circuit, wherein the fourth switch transistor has a first end connected with the second end of the third switch transistor, a second end configured to be grounded, and a control end connected with the control circuit.

2. The charging circuit of claim 1 , wherein the switch transistor in the first circuit is metal oxide semiconductor field effect transistor (MOSFET).

3. The charging circuit of claim 1 , wherein the second circuit comprises a rectifier circuit and a filter circuit.

4. A mobile terminal, comprising a charging interface, a battery, and a charging circuit, wherein the charging circuit is coupled between the charging interface of the mobile terminal and the battery of the mobile terminal and configured to charge the battery of the mobile terminal, and the charging circuit comprises a first circuit, a magnetic coupling element, and a second circuit connected in series between the charging interface and the battery, wherein

the first circuit is configured to receive a first current from the charging interface and convert the first current to a second current with at least one of a magnitude and a direction changed, wherein the charging interface is a universal serial bus (USB) interface and the first current is a direct current (DC);

the magnetic coupling element comprises a first coil and a second coil, the first coil is connected with the first circuit, the second coil is connected with the second circuit, and the first coil and the second coil are separated from each other to disconnect a direct current path of the charging circuit when the first circuit fails, wherein the magnetic coupling element is configured to transfer energy from the first coil to the second coil in an electromagnetic induction manner by utilizing the second current with at least one of a magnitude and a direction changed when the first circuit outputs the second current, to generate a third current at the second coil;

the second circuit is configured to adjust the third current to a fourth current suitable for battery charging to charge the battery; and

the first circuit comprises a full-bridge circuit and a control circuit controlling the full-bridge circuit, and the full-bridge circuit comprises a first switch transistor, a second switch transistor, a third switch transistor, and a fourth switch transistor, wherein the first switch transistor has a first end configured to be connected with the charging interface, a second end connected with a second end of the first coil, and a control end connected with the control circuit, wherein the second switch transistor has a first end connected with the second end of the first switch transistor, a second end configured to be grounded, and a control end connected with the control circuit, wherein the third switch transistor has a first end configured to be connected with the charging interface, a second end connected with a first end of the first coil, and a control end connected with the control circuit, wherein the fourth switch transistor has a first end connected with the second end of the third switch transistor, a second end configured to be grounded, and a control end connected with the control circuit;

wherein the mobile terminal is operable in a normal charging mode and a fast charging mode, and a charging current is larger in the fast charging mode than in the normal charging mode.

5. The mobile terminal of claim 4 , wherein the switch transistor in the first circuit is metal oxide semiconductor field effect transistor (MOSFET).

6. The mobile terminal of claim 4 , wherein the second circuit comprises a rectifier circuit and a filter circuit.

7. The mobile terminal of claim 4 , wherein the charging interface is a USB interface.

8. The mobile terminal of claim 4 , wherein the battery is a lithium battery.

9. The mobile terminal of claim 7 , wherein the battery is a lithium battery.