Patent ID: 7777457

Claim:
A method of controlling a constant frequency current-mode buck-boost converter, the buck-boost converter including an inductor, a first switch connected between an input terminal of the converter and a first end of the inductor, a first current control means connected between the first end of the inductor and ground, a second current control means connected between a second end of the inductor and an output terminal of the converter, and a second switch coupled between the second end of the inductor and ground; the method comprising: deriving a feedback signal from the output terminal; sensing a signal representative of current in the inductor to provide a sensed current signal; providing first and second ramp signals, the first ramp signal for use in controlling buck operation through at least the first switch, the second ramp signal for use in controlling boost operation through at least the second switch; and generating drive signals to repeatedly open and close at least the first switch and second switch at individual duty cycles determined on the basis of the feedback signal, the sensed current signal and the first and second ramp signals; wherein the first and second ramp signals are mutually offset to one another in time, in such a way as to allow said sensing step to be performed only while the first switch is closed.