Power in the pocket, part 1

a simple PWM amplifier

There are plenty of designs for simple audio power amplifiers. These generally have a class-AB or class-B topology. Here we present a very compact class-D design that can be powered from four AA batteries and because of its relatively high efficiency can elicit quite a few decibels from a loudspeaker.

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Materials

080277-PCB.pdf

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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PCB

Download Gerber file: 080277-1-V30

Extra info / Update

Technical specifications
- 1 W into 8 O, 1.7 W into 4
- Class-D
- Power supply 6 to 9 V (4x AA cell)
- Very compact
- Simple construction without SMDs

Component list

Resistors
R1 = 470k
R2 = 10k
R3 = 12k
R4,R5 = 220
R6 = 8O2
Capacitors
C1 = 10µF 63V, radial, 6mm diam.
C2 = 100nF ceramic, lead pitch 5mm
C3 = 100µF 40V, radial, 8mm diam., lead pitch 0.1" (2.5mm)
C4 = 270pF, ceramic, lead pitch 0.2" (5mm)
C5 = 330nF, MKT, lead pitch 0.3" (7.5mm)
C6 = 220nF, MKT lead pitch 0.3" (7.5mm)
C7 = 1000µF 25V, radial, 10mm diam., lead pitch 0.2".
Inductors
L1 = 40µH 2A axial (mount vertically) e.g. Epcos type B82111EC23; Farnell # 9753354
Semiconductors
D1,D2 = BAT85
T1 = IRFU9120NPBF (TO-251AA/I-PAK, International Rectifier) e.g. Farnell # 8659206
T2 = IRLU120NPBF (TO-251AA/I-PAK, International Rectifier) e.g. Farnell # 8651345
IC1 = 4050
Miscellaneous
S1 = 1 make contact, 1A min. (not on PCB)