Systems, devices and methods using three separate switching phases for a buck-boost regulator are disclosed. The regulator may operate in a boost mode, a buck mode or in a buck-boost mode. The output voltage remains constant through mode changes and the ripple voltage is well-controlled. If the input voltage is lower than the output voltage by a first threshold, the regulator operates in boost (step-up) mode. If the input voltage is higher than the output voltage by a second threshold, it operates in buck (step-down) mode. The regulator operates in the buck-boost mode when the difference between the input and output voltages is within a certain range.