Resonant Gate-Drive Circuits for High-Frequency Power Converters

The development trend of power converters motivates the pursuit with high density, high efficiency, and low cost. Increasing the frequency can improve the power density and lead to small passive elements and a fast dynamic response. Each one of these power converters must be driven by a gate-drive circuit to operate efficiently. Conventional gate-drivers are used up to frequencies of about 5 MHz and suffer from switching losses. Therefore, the development of switch-mode power supplies (SMPS) operating at high frequencies requires high-speed gate drivers. The presented research in this dissertation focuses on analysis, design, and development of new types of resonant gate-drive circuits to drive power transistors at high frequencies. Three proposed topologies are presented in this dissertation. Two topologies are single-switch ZVS gate-drive circuits. The attractive features of the two circuits are : (a) suitable to drive a low-side power transistor, (b) capable of operating at high frequencies with quick turn-on and turn-off transitions, (c) low power loss due to zero-voltage switching in the driving switch, (d) a significant increase in gate-source voltage of the driven switch with respect to the input voltage, (e) small energy storage components, and (f) designed to operate at switching frequency 20 MHz and a supply voltage of 4 V. The third presented topology is a class-D resonant gate-drive circuit. A series resonant circuit is formed by the resonant inductor and the input capacitance of the MOSFET to achieve the charge and discharge process of the transistor input capacitance. The proposed circuit can be used as a gate-drive circuit to drive low-side or high-side power switches operating at 6.78 MHz. In each above topology, detailed steady-state operation and derived expressions for the steady-state waveforms are presented. The analysis includes predicted power loss expressions in circuit components to estimate the overall losses in the gate-drive circuits. A design procedure of the proposed gate drivers is developed. The simulations and experimental results are given to validate the theoretical analysis. Finally, in the last chapter of the dissertation, the behavior of an air-core inductor operating at high frequencies is investigated. An appropriate model for the inductor is introduced to represent the effect of high frequencies on the inductor\u27s winding resistance. The analysis includes an expression to estimate the power loss in the air-core inductor. A detailed design methodology is presented to predict the dc and ac characteristic of the air-core inductor. A design example of an air-core inductor is given for switch-mode power gate driver operating at high frequencies