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555 Class-D Audio Amplifier

A novel use for an old-timer

Based on a Labs project | March 2013 | Find it here
555 Class-D Audio Amplifier
The celebrated ‘555’ IC was originally developed as a timer device, but over the years this golden oldie has been used in all sorts of other applications, including some never imagined by its inventors. This article describes a small class-D stereo audio amplifier built around the oscillator and modulation sections of a 555. The simple design makes it easy to build the circuit yourself.
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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor GREEN and GOLD members can exclusively download these files for free as part of their membership. Gerber files allow a PCB to be produced on an appropriate device available locally, or through an online PCB manufacturing service.

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Download the BOM list
The BOM (Bill of Materials) is the technically exhaustive listing of parts and other hardware items used to produce the working and tested prototype of any Elektor Labs project. The BOM file contains deeper information than the Component List published for the same project in Elektor Magazine. If required the BOM gets updated directly by our lab engineers. As a reader, you can download the list here.
Want to learn more about our BOM list? Read the BOM list article for extra information.
Component list
R1,R15 = 100kOhm
R2,R16 = 15kOhm
R3,R17 = 82kOhm
R4,R8,R18,R22 = 1kOhm
R5,R19 = 10kOhm
R6,R20 = 680Ohm
R7,R21,R29 = 2.2kOhm
R9,R23 = 18kOhm
R10,R24 = 470Ohm
R11,R25 = 100Ohm
R12,R26 = 330Ohm
R13,R27 = 8.2Ohm, 1W
R14,R28 = 2.7kOhm
R30 = 56kOhm
R31,R32 = 56Ohm, 1 W
P1,P2 = 2kOhm multiturn preset (Vishay Sfernice T93YB202KT20)
C1,C15 = 2.2µF 50V, 5mm or7.5.mm pitch (e.g. Panasonic ECQV1H225JL)
C2,C16 = 330pF 1%, polystyrene, 7,18mm pitch (e.g. LCR Components EXFS/HR 330PF ±1%)
C3–C6,C8,C10,C17–C20,C22,C24,C30,C32 = 100nF, X7R, 0.2’’ pitch
C7,C9,C21,C23 = 1nF MKT, 5mm pitch
C11,C25,C29 = 1000µF 35 V, radial, 12.5mm dia. 5mm pitch (e.g. Rubycon 35YXF1000MEFC12.5X25)
C12,C26 = 680nF polypropylene, 15mm pitch (e.g. Panasonic ECWF2684JAQ)
C13,C27 = 220nF metallized film (MKT), 5mm pitch
C14,C28, = 2200µF 35V, radial, 18mm diam. 5mm or 7.5mm pitch (e.g. Panasonic EEUTP1V222)
C31 = 10µF 100V, radial, 6.3mm diam., 2.5mm pitch
C33 = 47µF 35V, radial, 8.5mm max. diam., 2.5mm pitch
L1,L2 = 47µH, 21mOhm/8.5A, pot core type (Murata Power Solutions 1447385C)
L3 = 100µH, 35mOhm/5A ring core type (Würth Elektronik 7447070)
D1–D8 = 1N5819
D9,D10 = LED, red, 2x5mm rectangular
D11 = LED, red, 3mm
D12 = 15V/0.5W zener diode
D13 = 1N4148
T1,T3,T10,T12,T19 = BC547C
T2,T4,T11,T13 = BC557C
T5,T14 = BD139
T6,T15 = BD140
T7,T16 = 2N2222
T8,T9,T17,T18 = IRF530
IC1,IC2 = TLC555CP
IC3 = 7815
K1,K2 = 2-pin pinheader, 0.1’’ pitch
K3,LS1,LS2 = 2-way PCB screw terminal block, 0.2’’ pitch
RE1 = Relay, 24V, 1200Ohm, 8A, DPDT-CO (e.g. Finder
F1 = glass fuse, 2A(T), slow-blow, with PCB mount holder and cover
TP1,TP2 = 1 pin of pinheader
HS1 = heat sink for MOSFETs, aluminum plate 130 x 50 mm (5.1 x 2 inch), 1-2mm thick
4 x isolating washers for TO-220 case (e.g. Bergquist SIL-PAD K-10, .006’’, TO-220)
4 x isolating bush, 3mm
Heat sink for IC3, 30K/W (e.g. Fischer Elektronik SK 12 SA 32)
Switch-mode power supply, sec. 24V, 2.5A min.
PCB # 130144-1 [1]

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