Constant frequency synthetic ripple power converter

Abstract

A novel method to operate synthetic ripple switching power converters at constant frequency is presented. The method includes the generation of a clock signal and the summing of a ramp signal to a DC voltage reference to be compared to a synthetic ripple signal. The ramp signal is synchronous with the clock signal. A minimum on-time or minimum off-time type of control is implemented. The switching frequency is constant. The presented approach provides significant advantages with respect to the more traditional means of utilizing hysteretic approaches combined with frequency control circuits. The switching frequency can be as high as the one obtained for a hysteretic power converter, the load and line transient response is comparable with or better than the one achieved with hysteretic approaches. The stability is obtained by adapting the slope of the ramp signal in order to obtain the adequate gain of the system. The method is presented for buck and boost hysteretic high frequency switching power converters, but can be utilized also for buck-boost converters. The general method can be utilized also for multiphase switching power converters. A non clocked variant of the novel circuit topology is also presented to improve load and line transient performance.

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