A buck power converter is circuitry to operate a buck power stage 10 as shown in FIG. 1 to step down an input voltage Vin to an output voltage Vo for a load Rload, and a boost power converter is circuitry to operate a boost power stage 12 as shown in FIG. 2 to step up an input voltage Vin to an output voltage Vo for a load Rload. Unfortunately, a conventional buck power converter or boost power converter is inadequate to provide a stable voltage for a system, for example a portable device, that uses a battery as its power source Vin because a battery is unable to provide a stable voltage all the time during its lifetime.
Since the voltage of a battery descends with exhaustion of its power, a system using a battery as its power source requires a power converter switchable between a buck mode and a boost mode. A buck-boost power converter is circuitry to operate a buck-boost power stage 14 as shown in FIG. 3 to step down or step up an input voltage Vin to an output voltage Vo for a load Rload. However, such a buck-boost power converter produces a negative output voltage Vo and is thus unsuitable for some applications. Therefore, a buck-boost power stage 16 as shown in FIG. 4 was proposed, by which a positive output voltage Vo is generated from an input voltage Vin. For operating the buck-boost power stage 16 shown in FIG. 4, there have been proposed many control circuits and methods, for example, U.S. Pat. Nos. 6,166,527 and 7,518,346. Nevertheless, these arts are still not sufficient for users' demands.
Therefore, it is desired a novel control circuit and method for a buck-boost power converter.