Implementation of a New Structure for a Closed-Loop Class D amplifier Sérgio Sousa Victor M. E. Antunes V. Fernão Pires J. Fernando Silva Escola Sup. Tecno. Setúbal Instituto Politécnico Setúbal CIEEE Escola Sup. Tecno. Setúbal Instituto Politécnico Setúbal CIEEE Escola Sup. Tecno. Setúbal Instituto Politécnico Setúbal CIEEE Instituto Superior Técnico Univ. Técnica de Lisboa CIEEE sergio.sousa@netvisao.pt vantunes@est.ips.pt vpires@est.ips.pt fernandos@ist.utl.pt Abstract - In this paper is proposed the implementation of a novel structure for a Class D amplifier based on a robust closed loop control. The proposed control it is based on a multi level sliding mode controller. This allows of being able to converge to a stable status in spite of unknown or nonlinear elements present in the amplifier. The methods and systems proposed are also described. Several simulation results are presented. The obtained results confirm the potential of this configuration, as it is shown in the last part of this paper. I. INTRODUCTION In the last years audio power-amplifiers based on class D output stages have been used as an alternative to conventional class A/B designs. The advantages of using a class D output stage include high efficiency and small dimensions due to the reduced needs for heat sinking. The classical class D audio amplifier uses a full bridge switching inverter and an analog signal processing to form the PWM signal by comparing the audio signal with a high frequency saw tooth or triangle signal that acts as a carrier signal. The resulting binary signal of the comparator feeds a suitable set of power switches connected to the power supply. In order to suppress the inherent high frequency components of the PWM process, an LC low pass filter separates the output of the switches and the load. The fundamental problem of open loop PWM Class D audio power amplifiers is the inherent non-linearity and low resolution of the PCM/PWM modulation [1]. To reduce the introduced total harmonic distortion, several methods have been proposed [2-9]. Another approach to attenuate those problems is to use a closed loop approach. There are a number of closed loop systems built for class D amplifiers, used mainly to reduce nonlinear parameters from the modulation system, semiconductors, and output filter [10]. The advantages of a closed loop over an open loop controlled system are well known [11]. This paper describes a closed loop controlled class D amplifier. More specifically, the control is based in a robust configuration – a multi level sliding mode controller. The sliding mode controller, along with other robust controllers, has the distinctive advantage of being able to converge to a stable status in spite of unknown or nonlinear elements present in the amplifier [12], among other advantages. It has been establish that sliding mode control can be used with advantages over PWM modulation in class D audio amplifiers. Instead of a typical full bridge switching inverter it will be used a different power structure. The proposed power structure together with the multi level sliding mode control allows obtaining audio amplifiers with high performance for almost any application. . II. PROPOSED SYSTEM A simplified block diagram of a typical Class-D amplifier is shown Figure 1. A low power audio input signal is fed into a pulse-width modulator. The resulting binary PWM- waveform is then power amplified. The amplified PWM- signal is applied to a low pass-filter. The obtained result is the power audio signal. Figure 1. Basic Structure of a Class-D Audio Amplifier. However, typical class D audio power amplifiers present some problems as referred in the introduction. In this way, a sliding mode controller have been introduced into these systems [13] due to the advantage of being able to converge to a stable status in spite of unknown or nonlinear elements present in the amplifier. Fig. 2 shows a simplified block of this system. Figure 2. Basic Structure of a Class-D Audio Amplifier with a sliding mode controller. POWERENG 2009 Lisbon, Portugal, March 18-20, 2009 978-1-4244-2291-3/09/$25.00 ©2009 IEEE 26