A Dual-Channel Four-Switch Resonant Gate Driver for LLC Secondary Side MOSFETs

Due to its superior soft-switching characteristics, the LLC resonant converter achieves efficient power transmission at high frequencies and is extensively utilized in high power density applications. Conventional drivers exhibit loss that increase proportionally with frequency, resulting in excessive driving loss at high frequencies. To address this, a dual-channel four-switch resonant gate driver (DCFSRGD) is introduced in this paper to drive the secondary-side MOSFETs of the LLC. The proposed DCFSRGD can adjust duty cycles and switching frequencies through appropriate control timing, achieving 82% energy recovery compared to conventional drivers. Unlike other resonant gate drivers used in LLC-DCX applications, this DCFSRGD also facilitates changes in duty cycle and frequency, making it suitable for variable frequency LLC applications. This paper details the operational principles and optimized design methods of the proposed driver. A prototype with a resonant frequency of 1.3 MHz was constructed to validate the effectiveness of the proposed resonant gate driver.

I. Introduction

The LLC resonant converter, renowned for its excellent soft-switching characteristics, achieves zero-voltage switching (ZVS) for primary-side MOSFETs and both ZVS and zero-current switching (ZCS) for secondary-side synchronous rectifiers across the full load range [1] - [3]. This capability, combined with its operation at high frequencies, renders the LLC converter ideal for applications requiring high power density. As the switching frequency reaches the MHz range, the driving loss of MOSFETs become a critical factor limiting further enhancements in efficiency and power density, particularly in applications characterized by low voltage and high current output [4] - [7]. In such scenarios, paralleling multiple MOSFETs on the secondary side often becomes necessary to reduce conduction loss in synchronous rectifiers, which, in turn, increases the overall system driving loss.