Class-BD Audio Amplifiers with Common-Mode Free Output

J. Jasielski, S.W. Kuta (Higher Vocational School Tarnow, Poland), W. Machowski (AGH Univ. of Science and Techn., Poland)

A new topology of the Class-BD amplifier is proposed. It is composed of the typical H-bridge output stage with four MOSFETs controlled by the optimal NBDD PWM signals and two additional switches separating the H-bridge from the power supply during the time intervals in which either high-side or low-side MOSFETs of the H-bridge are closed at the same time. The differential output of the presented amplifier has the same audio performance as that one using the optimal NBDD modulation, moreover, the power MOSFETs creating the new output H bridge are switching at the same frequency as its prototype. The proposed Class-BD amplifier keeps the CM output constant, thereby removing a major contributor to radiated emissions. Basic feasibility study of the proposed configuration has been performed and compared with the configuration of the Class-BD amplifier using CM Free PSCPWM modulation known in literature on the subject. Experimental models of the considered in the paper Class-BD audio amplifiers have been realized using digital audio MOSFETs IRF6775MTRPbF, single-output gate drivers with self-boost charge pump bias supply and with capacitor-based signal isolation for floating single-output gate drivers. Simulation results are presented.