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Abstract:The full-bridge topology is generally used in the post stage of inverter, to realize dc-ac voltage conversion. Inherent shortcomings of full-bridge such as high-side switch driving, prone to shoot-through and substantial power loss are inevitable. A topological solution is proposed in this letter, by means of improving the original coupledinductor Watkins-Johnson topology into dual low-side switch version and conducting synchronous control. Theoretical analysis and experimental results indicate that the improved topology is capable of generating pure sinusoidal ac output. The merits include ease of driving, low power loss, nonpulsating terminal currents, immunity to shoot-through, simple control strategy and so forth.

In the field of non-isolated light-emitting diode (LED) driver, the omnipresent buck-based LED constant current driver shows poor efficiency in occasions of high step-down ratio due to the marginal operating duty cycle. In order to overcome such drawback and to provide an alternative topological scheme for an LED driver, a Watkins-Johnson topology-based solution is proposed in this paper, by improving the original circuit structure into a dual low-side power switch version and introducing a feedback network for regulating the output current to a constant level. Theoretical analysis, including accurate model construction, steady-state analysis, dynamic analysis, and design consideration, is conducted. Also, an experimental prototype is realized to drive all kinds of LED arrays for acquiring electrical parameters and evaluating performance. The innovative points include invoking the low-side-ize approach to realize the power circuit transformation, and furthermore, the Watkins-Johnson topology is first applied to the constant current power supply. The proposed LED driver holds salient features of low-terminal current ripple, ease of driving, highvoltage conversion ratio tolerance, and inherent energy recovery functionality. The application scope covers low-voltage dc input or automotive lighting use.INDEX TERMS Constant current, LED driver, synchronous control, Watkins-Johnson topology.

Conventional high-frequency non-isolated inverter is generally composed of two stages, the step-up stage and the voltage inversion stage, and independent control strategy must exert on each stage. In order to solve the shortcoming, a topological solution (L3 topology) is proposed in this letter, combining the structure of the boost topology and the improved Watkins-Johnson topology to a single stage, realizing voltage step-up and inversion with only three ground-side power switches and single control signal. Theoretical analysis and experimental results validate the feasibility. The merits include ease of driving, small port current ripple, high efficiency, simple control strategy and so forth.

This paper proposes a small-signal modeling method for building an LLC half-bridge resonant converter. In recent years, the LLC half-bridge resonant converter has attracted the attention of many researchers because of its high-power conversion efficiency and high-power density. Generally, the LLC half-bridge resonant converter consists of many passive components, including stray and parasitic elements, resulting in a high-order system. Because the fundamental harmonic approximation (FHA) method for an LLC resonant converter only considers the fundamental harmonic and neglects higher harmonics, it is not accurate and introduces large errors in a higher-order system. In this paper, according to the operation principle of the LLC half-bridge resonant converter, a small-signal model is established. Based on the small-signal model, the input-to-output and control-to-output transfer function is derived. The experimental result verified that the proposed model yields a high accuracy, thereby highlighting the usefulness and versatility of the proposed model over other existing models.