Constant frequency ripple regulator free from sub-harmonic oscillation

This paper presents a constant frequency ripple regulator free from sub-harmonic oscillation. In order to obtain good transient responses for input voltage and load current changes, a new PWM control method with inherent derivative characteristics is proposed. The ripple regulator presented in this paper consists of a comparator, a simple RC network and an error amplifier, and it can be synchronized with an external clock signal. Since the converter operates at constant frequency, it is easy not only to design an output filter but also to apply to multi-phase converters. Furthermore, the ripple regulator using the proposed method is free from sub-harmonic oscillation even though it operates at constant frequency. As a result, good transient performances are not spoiled since an additional ramp voltage is no longer necessary.