A current steering circuit for controlling a branch current flowing through a branch is provided. The branch is coupled to a first main switch. The current steering circuit includes a sensing device, a first auxiliary switch and a control unit. The sensing device is coupled to the branch and arranged for sensing the branch current to generate a sensing result. The first auxiliary switch is coupled in parallel with the first main switch. The control unit is coupled to the sensing device and the first auxiliary switch, wherein while the first main switch is turned on, the control unit generates a first switch control signal to the first auxiliary switch, and adjusts a duty cycle of the first switch control signal according to the sensing result in order to adjust the branch current.