High-Efficiency Control Techniques For Modern Integrated DC-DC Converters

With the increasing application of DC-DC converters in electronic devices, conversion-efficiency should be improved to help achieve high efficiency in energy utilization, especially in the 21-century society which appeals to energy saving.The three main causes of power consumption in DC-DC converter are conduction power loss, static power loss and dynamic power loss (including driving loss and transition loss at power transistor). The impact of each power loss on the conversion efficiency differs in various applications, and specific control techniques should be adopted accordingly to maximize the efficiency.Conduction power loss is the chief factor of efficiency degradation when the output current is high and the load relatively fixed, such as solid-state LED lighting, and thus its reduction should be the emphasis in such cases, where average current sensing based on pulse-level-modulation (PLM) demonstrates unusual merits. The advantage of this method is closely studied, based on which a control scheme is proposed to achieve high efficiency and high accuracy in floating Buck converter for LED lighting. The proposed control scheme employs adaptive off-time (AFT) control to achieve quasi-fixed switching frequency and PLM control scheme for high accurate average current control. Moreover, to speed up system recovery from LED dimming off, standby or failure, a static analog memory circuit is proposed to achieve long-term high-accuracy analog storage of control information.The reduction of the static power loss and driving loss at power transistor is crucial when the voltage level is low, say below 20V, with variable input/output condition. To achieve this goal, multi-mode control technique and multi-conversion-mode control technique are applied. For the former, a case study is carried out in peak current mode control, a successful high-efficiency PWM/Burst dual-mode Buck converter design. For the latter, a control method for single-inductor four-switch Buck-Boost converter is proposed, with tri-conversion mode and constant on-time control method, achieving high efficiency over the entire input voltage range and load range. Meanwhile, adaptive on-time control is suggested to overcome the problem that frequency varies with input/output voltage condition in conventional constant on-time control. Furthermore, a ripple generation circuit without ESR is proposed to eliminate the power loss by ESR, increasing the conversion efficiency all the more.Reducing dynamic power loss and static power loss is the priority in applications where the voltage level is high. Its realization relies on soft switching and multi-mode control technique. In a case study on flyback converter, a control method is proposed for high efficiency conversion over the entire load range, with quasi-resonant technique and multi-mode control method. Meanwhile, using integration technology, the static power loss by the controller can be controlled, reducing the standby power of the converter.Through integrated circuit (IC) design, computer-aided simulation and IC tape-out, the above proposed control methods have been successfully verified.