Switching converters such as buck, boost or buck-boost converters operate based on the cyclic magnetization and de-magnetization of an inductor associated with the respective increase and decrease of inductor current. The control of the magnetization and de-magnetization phases relies on a pair of power switches often referred to as main switch and synchronous rectifier switch. In operation the main switch is used for increasing the current of the inductor and the synchronous rectifier switch is used for decreasing it. Such switching converters rely on a careful timing operation of the main switch and the synchronous rectifier switch; when one of them is open the other is closed and vice versa.
Such DC-DC converters may be operated under various load conditions. When operating in light load conditions, conventional converters are configured to turn off the synchronous rectifier switch at a time when the inductor current decreases to a predetermined value. If the predetermined value is set to zero, the converter can only deliver a positive current to the load and the output voltage increases at every cycle. A so-called pulse skip method may be implemented to prevent the output voltage from increasing above a certain level. However, pulse skipping techniques are not suitable for applications requiring fixed switching frequencies. Alternatively, the predetermined value may be set to a negative value to guarantee regulation of the output voltage even when there is no load current. However this approach lowers the efficiency of the system.
USPTO Backgrounds
USPTO Backgrounds