Digital Controller for Optimized Efficiency and Extended Operating Range in High-Frequency Quasi-Resonant dc-dc Buck Converters

High-frequency, low-power dc-dc converters operated in the hundreds of kHz to multi-MHz range present a number of benefits such as fast transient response and reduced passive components. Drawbacks associated with switching and capacitive losses due to the increased switching rate can usually be mitigated by the use of resonant topologies with a softswitching operation. However, efficiency optimization is typically guaranteed for a narrow range of operating conditions. To address such issue, this paper presents a quasi-resonant buck converter (QRBC) with a low-complexity digital controller which minimizes the voltage across the active switch at turn-on on a switching cycle basis. In addition to efficiency optimization, the proposed technique extends the input voltage operating range over more traditional constant off-time controllers. Furthermore, a beneficial side effect of the proposed technique is a compression in the switching frequency variation range. Simulations and experimental results are reported for a proof-of concept 500 kHz, 5V-to-3:3V, 500mA discrete prototype with extensive sensitivity analysis against load current variations.