Small-signal analysis and design of constant frequency V2 peak control

This paper investigates the small-signal model and design considerations for constant frequency V² peak control. The factorized small-signal control-to-output transfer function is investigated, and the cause of the double poles is explained. Stability criterion is obtained, and design considerations are analyzed for different duty cycle applications, as well as different types of capacitors. To solve the instability problem, two types of compensations (either by adding an external ramp or a current ramp) are examined. The effect of the external ramp and the current ramp are analyzed, and design considerations are given based on the small-signal model. The external ramp is good enough to get a well-damped performance when feedback strength is strong (for example, when employing OSCON caps). However, current ramp is necessary to achieve good dynamic performance when feedback strength is weak (for example, when employing Ceramic caps). The small-signal analysis is verified with a Simplis simulation and experimental results.