Digital control method for improving light-load efficiency of asymmetrical half-bridge flyback converter

The traditional control method of asymmetric half-bridge flyback converter (AHBFC) is to use complementary PWM control. Under light load, due to the long turn-on time of its clamping tube, the primary side has large turn-on loss and cycle loss, and the converter efficiency is low. In order to solve the problem of low light-load efficiency, a digital control method based on TMS320F28335 is proposed. Non-complementary PWM control is adopted. The zero-crossing point of excitation current is estimated by control algorithm combined with the inductance voltage-second balance relationship. The converter works in intermittent mode, thus greatly reducing the conduction loss and circulating loss at the primary side of the transformer. Before the main switch is turned on, the auxiliary pulse is introduced to make the power switch zero-voltage switching (ZVS), which reduces the switching loss. The main loss of light load under the complementary control is analyzed, the working principle and design flow of the proposed control method are given, and the method is applied to a digital power supply prototype with input voltage of 48 V and output of 12 V/100 W. The experimental results show that under light load, the converter can realize zero voltage turn-on of two switches with this control method. Compared with the traditional complementary control method, the conversion efficiency is improved by 3%~11%, and the no-load current is reduced by 37.5%.