| CPC H02J 7/0013 (2013.01) [H02J 7/00034 (2020.01); H02J 7/0029 (2013.01); H02J 7/00714 (2020.01); H02J 7/02 (2013.01); H02J 2207/20 (2020.01)] | 22 Claims |

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1. A USB charging system, the charging system comprising:
a first AC-to-DC conversion unit configured to generate a first voltage and a first current;
a second AC-to-DC conversion unit configured to generate a second voltage and a second current;
a first USB output port corresponding to the first AC-to-DC conversion unit;
a second USB output port corresponding to the second AC-to-DC conversion unit;
a switch connected to the first AC-to-DC conversion unit and the second AC-to-DC conversion unit; and
a control chip connected to the first AC-to-DC conversion unit and the second AC-to- DC conversion unit and configured to open the switch and close the switch;
wherein the control chip is further configured to:
determine whether the first USB output port is connected to a first load device and whether the second USB output port is connected to a second load device;
if the first USB output port is connected to the first load device and the second USB output port is not connected to the second load device,
sample the first current of the first AC-to-DC conversion unit;
determine whether the first current flows out of the first AC-to-DC conversion unit;
if the first current flows out of the first AC-to-DC conversion unit, determine whether the first current is larger than a first predetermined threshold in magnitude; and
if the first current flows out of the first AC-to-DC conversion unit and the first current is larger than the first predetermined threshold in magnitude, close the switch.
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