Combined_Power_Supply_And_Audio_Amplifier.pdf

(59 KB) Pobierz
design
ideas
Circuit combines power supply and audio amplifier
Susanne Nell, Breitenfurt, Austria
he circuit in
Figure 1
can help if
110 OR 220V AC
MAIN SUPPLY
36V DC
you must transfer dc power and au-
24V DC
1
BRIDGE
dio over a pair of copper wires. One
470 F
IC
1
2
+4
2
+
application for such a circuit is a low-cost
V
IN
LM317 V
OUT
1
+ C
1
T
2
ADJ
1
door-opening system with speech input.
15 F
TRANSFORMER
LOAD 2
+
The circuit uses only one IC, the well-
150
680 F
3
LOUDSPEAKER
2
known LM317, a low-cost power-
Figure 1
1
supply regulator. Using this chip,
WM34
R
P
you can modulate the adjustment-pin in-
100k
ELECTRET
MICROPHONE
put with the audio signal from an electret
condenser microphone, connected be-
tween the output and the adjustment ter-
A novel circuit uses the adjustment pin of a regulator IC to provide audio amplification.
minals of the IC. The LM317 regulates
the output in such a way that the voltage must follow the voltage on R
P
, you obtain the microphone signal. For proper oper-
on the microphone is always 1.25V dc. a low-impedance audio signal riding on ation, the LM317 needs to deliver a min-
imum current of 4 mA from its output
This application uses a WM34 electret the output dc voltage.
The microphone directly modulates terminal. If your design uses no loud-
microphone, which comes in a standard
10-mm capsule from Panasonic and is the adjustment pin, so a smoothing ca- speaker, you can connect a load resistor
common in low-cost equipment. You can pacitor, such as C
1
, for noise and hum to sink this 4 mA. Designs using low-im-
use nearly any electret capsule, because does not influence the level of the audio pedance loudspeakers must also have
the well-regulated voltage on the micro- signal. C
1
shunts some of the audio sig- load resistors. You must add the ac cur-
phone never exceeds 1.25V. Every electret nal to ground, but the LM317 compen- rent in the audio signal to the minimum
capsule contains an integrated JFET- sates for the loss with internal gain. To current requirement of 4 mA. For an 8
based impedance converter that trans- avoid excessive losses in the LM317, use loudspeaker, you need a minimum resis-
lates speech into a current flowing from a capacitor with as low a value as possi- tive load of 470 to avoid distortion.
the source to the drain terminal. This ble. The circuit works well without a ca-
current through the microphone modu- pacitor, but values as high as 47 F do not
lates the voltage on the variable resistor, present a problem. Using R
P
, you can ad-
Is this the best Design Idea in this
R
P
. Because the output of the LM317 just the dc output voltage and the gain for
issue?
Vote at www.ednmag.com.
T

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika:

Zgłoś jeśli naruszono regulamin