Simple Digital Control Technique for a High-Frequency Quasi-Resonant Synchronous Buck DC-DC Converter

Low-power dc-dc converters employed in consumer applications are required to maintain a good efficiency over a wide operating range while keeping reduced footprint requirements. A digital control technique implementing an adaptive off-time modulation has been previously developed in order to extend the efficient operating range of quasi-resonant buck converter (QRBC) of the non-synchronous type. This paper addresses a corresponding adaptive off-time modulation technique for synchronous QRBCs, in which the problem of properly modulating the rectifying switch arises. Results indicate that, for a given converter design, application of the proposed approach extends the efficient operating range. More interestingly, from a design perspective, the proposed adaptive off-time modulation enables the use of smaller resonant inductance with negligible impact on the overall efficiency over a constant off-time controller. The proposed approach is described theoretically, and experimental results are reported for a 12 V-to-3.3 V, 1 A synchronous QRBC discrete prototype.