• on Audio/Video/Photography
  • Published in issue 6/2009 on page 58
About the article

Power in the pocket, part 1

a simple PWM amplifier

Power in the pocket, part 1
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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Gerber file

CAM/CAD data for the PCB referred to in this article is available as a Gerber file. Elektor 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. Elektor recommends its business partner Eurocircuits as the company of choice for its own prototypes and volume production in selected cases.

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

R1 = 470k
R2 = 10k
R3 = 12k
R4,R5 = 220
R6 = 8O2
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".
L1 = 40µH 2A axial (mount vertically) e.g. Epcos type B82111EC23; Farnell # 9753354
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
S1 = 1 make contact, 1A min. (not on PCB)

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