Anoptimal feedforward circuit with null audio susceptibility in feedback-controlled buck converter

Abstract

The ability to manage abrupt disturbances in input supply voltage and sudden fluctuations in load represents a fundamental requirement for DC-DC buck converters. While feedback control systems typically address such transients, certain applications necessitate even faster transient responses. This paper introduces an input voltage feedforward scheme (IVFS) integrated with voltage mode feedback controllers to enhance closed-loop performance. Relevant transfer functions resulting from the inclusion of the feedforward circuit are derived, and an optimal condition for audio susceptibility nullification is identified. This scheme ensures an additional attenuation in magnitude of audio susceptibility, in contrast to the buck converter without feedforward. In the time domain, the incorporation of IVFS results in a 20% reduction in percentage overshoot for a 12-8-12 step in supply voltage. Additionally, for a 12-15-12 step, the percentage overshoot and settling time are completely eliminated. Various active and passive parasitics are included in modeling of the buck converter to aid in designing the feedforward and feedback controller. A Type-III controller is employed as a feedback controller to assess the closed-loop performance. A hardware prototype is built to demonstrate the efficacy of the proposed feedforward scheme. The implementation of the entire circuit is straightforward due to its requirement of only a few discrete components, namely, analog multiplier, and error amplifier.