Desenvolvimento e validação experimental de uma placa didática para o estudo de classes de operação A, AB e B em amplificadores de sinais

Abstract

This work presents the development and experimental validation of a didactic audio amplifier board intended for the practical study of Class A, Class AB, and Class B operation. The proposal aims to bridge the gap between theoretical concepts in analog electronics and laboratory practice, allowing the observation of how output stage biasing affects the waveform, crossover distortion, total harmonic distortion, and circuit efficiency. The amplifier was developed based on a classic three-stage topology, composed of an input differential pair, a voltage amplifier stage, and a complementary output stage. The board was designed to operate nominally in Class AB, allowing Class B operation through a switching key and Class A operation by adjusting the bias current through the VBE multiplier. Computational simulations, printed circuit board assembly, and experimental tests with a resistive load were performed. The obtained results made it possible to verify the occurrence of crossover distortion in Class B, its reduction in Class AB, and the characteristic behavior of Class A, as well as to compare the operating classes in terms of estimated total harmonic distortion and efficiency. Experimentally, estimated THD values of 0.425 %, 0.535 %, and 0.605 % were obtained for classes A, AB, and B, respectively, while the corresponding efficiencies were 32.21 %, 48.96 %, and 51.32 %. Therefore, the developed board fulfills its didactic purpose, serving as a practical tool for teaching power amplifiers in analog electronics.