A Parabolic Voltage Control Strategy for Burst Mode Converters with Constant Burst Frequency and Eliminated Audible Noise

Abstract

To improve the conversion efficiency at light load, burst mode control is widely employed by power converters. One drawback of hysteresis burst mode control is that the burst frequency changes with different load, which would introduce audible noise to the system if burst frequency falls into audible frequency range. To solve the frequency variation and audible noise problems of burst-mode-controlled power converters, a parabolic voltage control method is proposed in this paper. A hysteresis burst-mode-controlled quasi-resonant boost converter is employed as an example. First, the operation principles of the boost converter are analyzed and the simplified circuit is obtained. Based on the simplified circuit, the frequency variation problem is studied and burst frequency change over different loads is calculated. Second, by analyzing the constitutive equations of the simplified circuit, inspired the derivation of parabolic current control, a pair of parabolic control carriers are obtained. The proposed parabolic carriers serve as the control band to achieve constant burst frequency, eliminating audible noise, and extending the light load efficiency to the whole load range. A comparison between parabolic voltage control and parabolic current control is conducted. It is found that parabolic voltage control can be seen as the dual of parabolic current control. In addition, the convergence process of the proposed parabolic voltage control is analyzed. The performance of the proposed control strategy is experimentally verified with prototype hardware.