POWER BACKUP CIRCUIT AND METHOD OF OPERATING THE SAME

A power backup circuit (100, 100', 100") provides a plurality of input power sources (Vinl, Vin2) to back up a load (200), wherein the input power sources (Vinl, Vin2) at least comprise a first input power source (Vinl) and a second input power source (Vin2). The power backup circuit (100, 100', 100") includes a first switch (12, 12'), a second switch (14, 14'), and a control unit (16). If the power source of the load (200) is determined to be changed from the first input power source (Vinl) to the second input power source (Vin2), the control unit (16) controls the first switch (12, 12') to be coupled to the second input power source (Vin2) and controls the second switch (14, 14') to be coupled to the second input power source (Vin2) after the control unit (16) effects a supply current flowing through a first power supply path (PI) and a second power supply path (P2) both coupled to the first input power source (Vinl) and the load (200) to be reduced below a current threshold.