Abstract
A systematic and simple approach to develop a 20 W audio frequency range switch mode amplifier is presented in this paper. A non-linear sliding mode (SM) technique-based low cost analog controller enables the realized amplifier to deliver highly linear and efficient operation throughout the audio frequency spectrum. The theoretical aspects and practical limitations in the design and realization of subsystems, such as the signal conditioning stage, power stage and sliding mode controller, are considered, while the viable solution is also stated and justified. The hardware realization scheme is also elaborated, based on which the laboratory prototype is fabricated. Hardware results with a 4 Ω resistive load are given on which the performance of the amplifier is evaluated. The total harmonic distortion (THD) below 1% and 73% efficiency at peak load make the amplifier well suited for high quality audio application.
Highlights
The clear and faithful sound of a home audio system is vital for a good listening experience
The gain setting resistor chosen is in the range of tens of ohms, the reason being that the low value of resistance introduces very little thermal noise voltage in the output
The functioning of each constituent block in the amplifier, design methodology and selection of components are discussed in sufficient detail
Summary
The clear and faithful sound of a home audio system is vital for a good listening experience. Linear amplifiers (Classes A, B, and AB) used in low-power audio applications offer high linearity but suffer from poor efficiency. Open loop architecture-based Class D amplifiers, though highly efficient, suffer from poor linearity. To realize a PWM-based closed loop controlled amplifier demands unrealistic open loop bandwidth, around 20 MHz, and a high frequency carrier generator for audio grade amplification. A non-linear controller, such as a hysteresis controller, has much wider control bandwidth, equal to switching frequency, in comparison to linear controller [11] Such an amplifier suffers from poor audio quality and the low disturbance rejection problem [6,11,12,13,14,15]. On the basis of the theoretical/practicals aspects, performance and shortcomings of the amplifier, a brief conclusion is given in Section 5 of the paper
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