Linear-non-linear control (LnLc) for DC-DC buck converters: stability and transient response analysis

Power supplies for last generation of microprocessors and DSPs must present low output voltage and fast transient response. The linear-non-linear control (LnLc control) was presented as a solution to improve the transient response in DC-DC buck converters. However, once the LnLc control has been analyzed, other important performances have been found such as, improving the stability of the system, improving the efficiency, reducing of the recovery time, making independent the bandwidth and the switching frequency; reaching all these performances with an easy implementation. In this paper, the features of the linear-non-linear control are described. It will be shown, how the LnLc improves the stability of a DC-DC buck converter modifying the open loop gain and phase as a function of the load current steps. To show this behavior the control transfer function (G/sub LnLc/) has been deduced. Several experimental results have been obtained in a synchronous rectifier buck converter to check its behavior. Thus, the novel LnLc control has been compared with the conventional voltage control under different conditions. Finally, the control transfer function has been obtained experimentally.