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Homemade Single-Supply Class D Amplifier w/ Bluetooth Jay Mok & Chase Stine In this project, we made a class D (A.K.A. PWM) amplifier. The class D amplifier offers lower power dissipation than other classes (A, B, AB) [5]. The reason is because the transistors are used as ideally lossless switches rather than as linear amplifiers. The input audio signal is amplified as follows: the input goes into a pre-amplifier for filtering and small signal amplification. Then, it is compared with a triangle wave and transformed into two copies of itself: the PWM signal and its inverse (i.e. phase shift of 180, negative of itself). The two PWM signals then are fed into a gate driver IC, which is able to turn MOSFET switches arranged in full-bridge configuration quickly. The amplified PWM signal is then low pass-filtered via lossless elements (L and C) and some other filtering configurations (snubbers). The speaker (subwoofer/midrange in our case) is then connected as a bridge-tied load across the full-bridge switching amplification stage. This is a conventional design for full-bridge class-D amplifiers [2]. We choose to built the amplifier from scratch out of discrete components, like in previous DIY projects [3, 4] rather than use an IC, which is what is usually done for commercial designs [6]. The Class-D amplifier is also powered by a singlesupply rather than dual-supplies as found often. Thus a positive power supply unit is also built from scratch. The design of the PSU is largely based on a previous design of a 10A unregulated power supply [7]. The major difference is the use of un-regulated supply rather than regulated supply based on recommendations from a book on audio amplifiers [8]. Originally we designed in amp feedback based on ideas from an old paper about amplifiers but due to stability issues, and severe time constraints, we decided to just use a non-feedback open-loop amplifier [1]. However, if given more time, we would have liked to include amplifier feedback. We use a bluetooth receiver 2 audio jack module, rather than build the bluetooth from scratch. We also use common IC and components found in university electronic laboratories, making this project not too difficult to implement. Furthermore, this capstone project combines knowledge from analog/digital electronic circuits, power electronics, signals and systems (filters), solid state (transistors), heat transfer (heat sinks), and electronic layout, making for a great chance to use what was learned in an undergrad EE curriculum. References 1.Slobodan Cuk and Robert Erickson, "A Conceptually New High-Frequency Switched-Mode Amplifier Technique Eliminates Current Ripple," Powercon 5, pp. G3.1-G3.22, May 1978. 2.Simon Tonnarelli, “100W Class D Amplifier”, Simon’s Satcom Page , April 2017 http://satcom.tonnarelli.com/ClassD.htm 3.GreatScottLab, “DIY Class D Audio Amplifier”, Instructables , 2018 https://www.instructables.com/id/DIY-Class-D- Audio-Amplifier/ 4.Cezar Chirila, “How to Build A Class-D Power Amp”, AllAboutCircuits , August 2016 https://www.allaboutcircuits.com/projects/how-tobuild-a-class-d-power-amplifier/ 5.Gaalaas, Eric. “Class D Audio Amplifiers: What, Why, and How.” , Analog Devices , June 2006, www.analog.com/en/analogdialogue/articles/class-daudioamplifiers.html. 6.NXP, “TDA8954 2 × 210 W class-D poweramplifier”, NXP Datasheet, December 24 2009, https://www.nxp.com/docs/en/datasheet/TDA8954.pd f 7.Vazerick, “<strong>Design</strong> and Implementation of a 10 Amp Linear Power Supply”, Instructables , 2016 https://www.instructables.com/id/10Amp-Linear- Power-Supply/ 8.Douglas, Self. “Audio Power Amplifier <strong>Design</strong> Handbook”, Newnes, 1996 44
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