A mixed-mode PWM controller

In this article, a mixed-mode (MM) PWM controller for dc–dc power converter topologies is presented and analysed. Compared to the conventional peak current-mode (PCM) controller, the proposed controller exhibits better results in terms of robustness towards load and reference voltage variations while maintaining better dynamic response. In the PCM controller, the control signal is a combination of inductor or, most often, switch current and a suitable compensation ramp which in the most common applications is constant. In the proposed controller, the constant compensation ramp has been replaced by a ramp voltage which is proportional to the output voltage taking into consideration the output voltage variations during load and reference transients. Consequently, the proposed controller, which exhibits the same advantages as with the PCM controller, additionally exhibits better load and reference performance for constant output voltage and output tracking applications without increasing the cost and the complexity of the control circuit. Finally, in order to verify the theoretical analysis and conclusions, both control schemes (i.e. PCM and MM) have been simulated and experimentally tested using a 75 W buck converter unit.