Patent ID: 8823340

Claim:
A control circuit adapted to control a buck-boost switching converter which has an input end, an output end, a ground end, an inductor with first end and a second end, a first switch connected to the input end and the first end of said inductor, a second switch connected to the first end of said inductor and the ground end, a third switch connected to the second end of said inductor and the ground end, and a fourth switch connected to the second end of said inductor and the output end, wherein an input voltage of the buck-boost switching converter is regulated as a steady output voltage, comprising: a feedback compensative circuit coupled to the output end and an output reference voltage to generate a compensative voltage based on the output voltage and the output reference voltage; a mode determinative circuit judging and generating a buck-boost operation mode signal based on the input voltage, the output voltage, and a mode reference voltage to determine a timing of an operation in the buck-boost mode; a waveform generating circuit generating at least a periodic waveform signal; a comparing signal generating circuit coupled to said waveform generating circuit, said feedback compensative circuit, and said mode determinative circuit to generate a first reference compensative voltage and a second reference compensative voltage based on the compensative voltage, and to generate a first reference waveform signal and a second reference waveform signal based on said at least one waveform signal; and a control signal generating circuit coupled to said comparing signal generating circuit, to generate a first, second, third, and fourth control signals to control said first, second, third, and fourth switches respectively based on said first and second reference compensative voltages and said first and second reference waveform signals so as to turn off the second switch during the first switch being on, turn on the second switch during the first switch being off, turn off the fourth switch during the third switch being on, and turn on the fourth switch during the third switch being off, and duty cycles of said first and third switches being identical and duty cycles of said second and fourth switches being identical during the operation in the buck-boost mode; wherein said comparing signal generating circuit is a level shifting circuit which comprises a resistor, and a current source connecting with said resistor in series.