FEBRUARY 2006 £3.80 - Index of
FEBRUARY 2006 £3.80 - Index of
FEBRUARY 2006 £3.80 - Index of
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th Problems Ton<br />
a<br />
JP400<br />
2<br />
1<br />
Audio Right In<br />
Right PWM-Bus<br />
from Current Limiter<br />
Disable<br />
(from Sheet 2)<br />
R425<br />
0Ohm<br />
C404 R426<br />
100pF 1Meg<br />
AGND AGND AGND AGND<br />
R435<br />
0Ohm<br />
BLI_R<br />
ALI_R<br />
PI-Controller<br />
Differential Input Analog Inverter<br />
Comparator<br />
C400<br />
R400<br />
47k<br />
470nF<br />
C401<br />
R401<br />
47k<br />
470nF<br />
C405<br />
100pF<br />
R419<br />
1.2k<br />
PGND<br />
+11V_D<br />
AGND<br />
100pF<br />
R409<br />
100k<br />
R410<br />
100k<br />
100pF<br />
+11V_A<br />
R411 R412<br />
100k 100k<br />
C409<br />
First impressions looked so<br />
promising! The Swiss lecturer<br />
in electronics Mr. Stefan Wicki<br />
<strong>of</strong>fered us a design for a power<br />
amplifier (the ‘CDAMP’) that he<br />
b<br />
had developed and uses as a<br />
construction project for his students<br />
at the University <strong>of</strong><br />
Applied Sciences in Aargau.<br />
The schematics and photos<br />
looked very promising and the<br />
prototype in a very small enclosure<br />
arrived in due course.<br />
The amplifier appeared to<br />
AGND<br />
have been well thought<br />
through, both externally as<br />
well as internally (see photo).<br />
All connections are located on<br />
the rear. On the front you will find two<br />
LEDs and the on/<strong>of</strong>f-switch. The amplifier<br />
is almost completely built with<br />
SMD parts and is well presented. The<br />
enclosure is made entirely from aluminium<br />
and as a result has a solid look.<br />
One detail that attracted our attention<br />
however was the way the input signal<br />
was routed from the input to the PCB.<br />
PGND<br />
2<br />
3<br />
C406<br />
U400A<br />
C402<br />
1IN-<br />
1OUT<br />
1IN+<br />
TS974<br />
D400<br />
ES1B<br />
100nF<br />
1<br />
+11V_A<br />
C407<br />
P400<br />
1Meg<br />
R437<br />
100nF 1Meg<br />
R413<br />
R414<br />
10k<br />
10k<br />
U400B<br />
AGND<br />
R421<br />
TP402 6.8k<br />
5<br />
6<br />
2IN+<br />
2OUT<br />
2IN-<br />
7<br />
diff. Out<br />
TS974<br />
C403<br />
R422<br />
R402<br />
22k<br />
47k<br />
100pF<br />
C415<br />
TP407<br />
Feedback<br />
H-Bridge Driver<br />
+11V_D<br />
C419<br />
1<br />
2<br />
3<br />
4<br />
5<br />
6<br />
7<br />
8<br />
100nF<br />
U402<br />
BHB BHO<br />
BHI BHS<br />
BLI BLO<br />
ALI ALO<br />
DEL VDD<br />
VSS AHS<br />
AHI AHO<br />
DIS AHB<br />
16<br />
15<br />
14<br />
13<br />
12<br />
11<br />
10<br />
9<br />
HIP4082IB<br />
14<br />
D401<br />
ES1B<br />
C420<br />
nc<br />
R415<br />
10k<br />
R416<br />
10k<br />
U400D<br />
4IN-<br />
4OUT<br />
4IN+<br />
TS974<br />
13<br />
12<br />
C416<br />
+11V_A<br />
nc<br />
R417 R418<br />
10k 10k<br />
C410<br />
BHO_R<br />
BHS_R<br />
BLO_R<br />
ALO_R<br />
AHS_R<br />
AHO_R<br />
100nF AGND<br />
100nF<br />
R403<br />
47k<br />
AGND<br />
Filter and Feedback<br />
to Current Limiter<br />
(to Sheet 2)<br />
Here two thin twisted litz-wires are<br />
used per channel, but these were seen<br />
to run right over the top <strong>of</strong> the output<br />
filters and final power stages!<br />
Schematic<br />
The amplifier was accompanied by a<br />
detailed circuit description, which<br />
Giesberts<br />
Design: Stefan Wicki<br />
PGND PGND<br />
PGND PGND<br />
Figure 1. One channel <strong>of</strong> the CDAMP designed by Mr. Wicki (a) and the accompanying triangle generator (b).<br />
C106<br />
100nF<br />
R112<br />
180k<br />
R122<br />
18k<br />
R103<br />
0Ohm<br />
+11V_A<br />
100nF<br />
R123<br />
1Meg<br />
R115<br />
270k<br />
AGND<br />
5<br />
1IN-<br />
4<br />
1IN+ GND1<br />
9<br />
10<br />
AGND<br />
R114<br />
330k<br />
R124<br />
8.2k<br />
C108<br />
100nF<br />
U103A<br />
LM319D<br />
2IN-<br />
3<br />
8<br />
2IN+<br />
GND2<br />
U103B<br />
LM319D<br />
+11V_A<br />
AGND<br />
explained the operation <strong>of</strong> all<br />
parts at length. In Figure 1a<br />
we show the schematic <strong>of</strong> one<br />
output stage (as drawn by the<br />
author). This clearly illustrates<br />
the design <strong>of</strong> the amplifier<br />
together with the triangularwave<br />
generator (Figure 1b).<br />
For clarity, we have left out all<br />
the other parts (other channel,<br />
power supply, protection,<br />
etc.). The audio signal goes to<br />
an input buffer first, and is<br />
then combined in a pi-style<br />
regulator with the feedback<br />
signal from the output stage.<br />
The signal then continues on<br />
to two comparators operating<br />
in anti-phase, which compare the voltage<br />
with the signal from the triangle<br />
generator. The comparators supply the<br />
PWM signal that is used to drive the<br />
final stage. The final stage consists <strong>of</strong><br />
a bridge <strong>of</strong> four power FETs. The loudspeaker<br />
is connected between the<br />
FETs via an output filter. A special Hbridge<br />
IC from Intersil provides the<br />
2/<strong>2006</strong> - elektor electronics 51<br />
C408<br />
R404<br />
47k<br />
R407<br />
47k<br />
R408<br />
47k<br />
AGND<br />
AGND<br />
+VS +VS<br />
TP414<br />
BGH<br />
BHO_R<br />
R429<br />
T400 T402<br />
6.8<br />
SI7852DP<br />
SI7852DP<br />
BHS_R<br />
TP410 TP411<br />
TP415<br />
BGL<br />
BHS AHS<br />
BLO_R<br />
R430<br />
T401 T403<br />
6.8<br />
AHO_R<br />
R431<br />
6.8<br />
AHS_R<br />
ALO_R<br />
R432<br />
6.8<br />
SI7852DP<br />
SI7852DP<br />
ILIM R+<br />
PGND<br />
10<br />
9<br />
R405<br />
47k<br />
U400C<br />
R406<br />
47k<br />
C414<br />
33pF<br />
B<br />
+11V_A<br />
3IN+<br />
3OUT<br />
3IN-<br />
TS974<br />
Triangle Generator (330kHz)<br />
+11V_A<br />
D104<br />
ZHCS1000<br />
12<br />
7<br />
R116<br />
820<br />
TP104<br />
Square Wave<br />
R118<br />
12k<br />
+11V_A<br />
R106<br />
47k<br />
R107<br />
47k<br />
AGND<br />
AGND<br />
C121<br />
100pF<br />
U104A<br />
2<br />
IN-<br />
OUT<br />
3<br />
IN+<br />
C109<br />
100nF<br />
LM7121<br />
8<br />
C417<br />
1nF<br />
C418<br />
1nF<br />
PGND<br />
TP403<br />
Audio-<br />
TP404<br />
Audio+<br />
R427<br />
4.7k<br />
R428<br />
4.7k<br />
H-Bridge<br />
6<br />
A<br />
R434<br />
SHUNT 22m/1W<br />
C110<br />
100nF<br />
TP416<br />
AGH<br />
TP417<br />
AGL<br />
+11V_A<br />
(from Sheet 1)<br />
R119<br />
10k<br />
R120<br />
10k<br />
AGND<br />
Triangle<br />
050183 - 12<br />
TP106<br />
Triangle<br />
Triangle<br />
(to Sheet 3/4)<br />
5<br />
1IN-<br />
4<br />
1IN+ GND1<br />
L400<br />
15uH/5.5A<br />
L401<br />
15uH/5.5A<br />
U401A<br />
LM319D<br />
3<br />
PGND<br />
U401B<br />
LM319D<br />
10<br />
2IN-<br />
9<br />
2IN+ GND2<br />
8<br />
PGND<br />
+11V_D<br />
12<br />
R420<br />
560<br />
7<br />
R436<br />
560<br />
Output Filter<br />
L402<br />
4.7uH/5.5A<br />
C421<br />
2.2uF/100V<br />
R423<br />
1.2k<br />
PGND PGND<br />
+11V_D<br />
R424<br />
1.2k<br />
L403<br />
4.7uH/5.5A<br />
C422<br />
2.2uF/100V<br />
TP405<br />
BLI<br />
TP406<br />
ALI<br />
PGND PGND<br />
BLI_R<br />
C431<br />
100pF<br />
ALI_R<br />
C432<br />
100pF<br />
C423<br />
0.47uF/100V<br />
C424<br />
0.47uF/100V<br />
R433<br />
4.7/1W<br />
Out R+<br />
C425<br />
68nF/100V<br />
Out R-<br />
Right PWM-Bus<br />
050183 - 11<br />
JP401<br />
2<br />
1<br />
Speaker Out Right
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