A control circuit of a multi-mode buck-boost switching regulator and a
method thereof are provided. The control circuit imposes ON/OFF timing
sequences on switches according to the relationship between two
controlling triangle waves and the load fluctuation. In each working
cycle of each mode of the regulator, at most two switches perform
switching operations. The control circuit is simple to design, which only
includes simple digital elements, such as comparators, logic gates etc.,
instead of complicated analog circuits.