Design Of High Power Audio Amplifier Based On Frequency Conversion PWM And Synchronization Technique

With high-quality components, complicated compensation circuit and strong negative feedback, Analog Power Amplifier can make the distortion be very low, however, the high efficiency has not been solved perfectly all the time, while the Class-D power amplifier under working, it is easy to achieve high efficiency.The PWM control technique is generally adopted in current Class-D amplifier. The sound signal output from amplifier equals to the modulated PWM signal. Thus, the function of PWM modulator can directly affects the fidelity of Class-D amplifier. Theoretically, the higher the carrier frequency of PWM modulator of audio amplifier, the better the acoustical effect is. Nevertheless, the exorbitant carrier brings about the matter of increasing the loss of the power tube, as well as the matter of enlarging the volume of thermal slug installed on the power tube. This problem reflects more serious on kilowatt high power amplifier. For example, a small power amplifier losing 1% just loses 10mW, in contrast, a kilowatt high power amplifier can reach to 10W. Moreover, the loss of 10mw doesn't need to install thermal slug, while the loss of 10W needs to install a volume of 6CM3 thermal slug.The Class-D high power audio frequency amplifier designed in this paper is mainly used for industrial kilowatt high power warning system. Although the requirement of acoustical amplifier is lower than professional acoustical amplifier, the requirement of efficiency and volume is higher than that. The carrier frequency of PWM is divided into three frequencies of f1, f2, f3, which meet the relation of f1<f2<f3. According to different variations of signal amplitude in different time period, modulate with different carrier frequency. Thereby, it can not only make the sound effect equal to the carrier frequency of f3, but also reduce the power loss.In addition, in order to avoid switching power providing energy for audio power amplifier become the source of interference of audio power amplifier in sound quality, synchronization technique is adopted in this paper for the frequency of switching power supply to keep consistent with the parameter of f1 in the same frequency and phase.