University of Twente Student Theses


Improving the linearity of a single stage boost converter audio amplifier

Oostewechel, P.S. (2016) Improving the linearity of a single stage boost converter audio amplifier.

[img] PDF
Abstract:Traditionally a two stage implementation (Boost converter + Class D) is used for low voltage supply to high output power audio amplifications. This work proposes an audio amplifier using a boost converter topology only. The goal is to improve overall system efficiency, reduce cost and increase boost converter linearity. In this work general linearization methods are adapted for use in a dynamic boost converter. A double loop feedback structure is used: an inner average current mode control loop sets the inductor current and the outer voltage loop controls the inner loop based on the required output voltage. The large signal behaviour of the current mode controlled converter shows square root behaviour, this square root is pre-distorted in the outer control loop to improve the linearity. A design is made for an amplifier which has a power gain of 5 x compared to a standard single ended class D amplifier. Simulations including parasitic elements show that the closed loop system with pre-distorter has a THD improvement of about 6 for low frequencies. The improvement decreases for higher frequencies, as the output capacitance of the converter reduces the load impedance. The decreasing load impedance influences the effectiveness of the pre-distorter. A prototype is created to compare simulation results to circuit implementation. The measured THD is 0.6 % with versus 1.3 % without pre-distorter at 10W output power. The results show that for a full bandwidth audio application it is not the best choice to use a boost converter as amplifier, as THD levels are quite high for higher frequencies. Performance is severely limited by the changing bias dependent dynamics, which limit the possible voltage loop gain. As subwoofer amplifier however, a boost converter amplifier is much more feasible.
Item Type:Essay (Master)
Faculty:EEMCS: Electrical Engineering, Mathematics and Computer Science
Subject:53 electrotechnology
Programme:Electrical Engineering MSc (60353)
Link to this item:
Export this item as:BibTeX
HTML Citation
Reference Manager


Repository Staff Only: item control page