A Control Actuation Concept for Self-Oscillating Resonant Converters

Abstract

This paper presents a new concept of controller actuator for Self-Oscillating Resonant Converters. Simplicity, robustness, and cost-effectiveness are amongst the main features that characterize this type of converter. Described as a self-oscillating system with intrinsic positive-type feedback, also known as the self-oscillating command circuit, it performs its gate-drive with fixed frequency and duty cycle. As a result, designers often disregard this converter as an explicit solution for closed-loop applications that require extra layers of control, due to its inherent inability to operate under controlled pulse frequency modulation without modifications. Thus, in this paper, the authors propose a robust, efficient and simple way of controlling the self-oscillating resonant converter through frequency modulation. The idea consists of varying the equivalent magnetizing inductance of the self-oscillating command circuit through the addition of an extra support winding, whose inductance is subject to a current-controlled Variable Inductor. Thus, through the injection of a small controllable DC current, it is possible to modify the self-oscillating frequency of this type of converter over a wide range of input voltage and load variation, maintaining the desired output level by PFM.