A reverse-current control circuit for high-reliability synchronous rectifier converter

Driven by cost and environmental protection issues, the requirements for light-load efficiency of power converters continue to increase, and low-power design under light load is required. The synchronous rectifier converter will generate reverse current under light load, and the reverse current control circuit effectively improves the light load efficiency. The traditional reverse current control circuit requires current sampling or a specific controller, which have not high reliability and low cost. A new reverse current control circuit is proposed for high-reliability applications, which can block light-load reverse current with only a few components and a general-purpose PWM controller. Firstly, the generation mechanism of the reverse current under light load is expounded, and the conclusion is drawn that the reverse current mainly flows through the synchronous freewheel. Secondly, the working principle of the proposed circuit is introduced in detail, the expressions of critical parameters are deduced, and the simulation is carried out. Finally, the circuit is applied to a 100W forward synchronous rectifier converter, and the parameters are designed. The test results show that the prototype can realize reverse current control under the entire input voltage range when applying the circuit. The light-load efficiency is increased by about 10%-20%, the no-load current is reduced by 87%, the load transient and load regulation of the output voltage is unaffected.