Senior Design Expo 2019

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, “Design 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 Design
Handbook”, Newnes, 1996
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