"NOISY" 1.5 Volt power supply?

[E Draisma]

Dear all,

First of all I tried the simplest approach suggested by some of you:
.. ___ Imax
.. 8-10V o-------|___|------o------>-----o ~1.4V
.. R |
.. |
.. |
.. V 1N4001
.. -
.. |
.. |
.. V 1N4001
.. -
.. |
.. |
.. ===
.. GND

This didn't work; the 8-10V power supply also stepped down to approx 2V. As
a result the amplifier connected to the MP3 player (and to the same power
supply) stopped working.
Next I tried the LM317 (see below & see attachment) This seemed to work as
it gave me 1,5V.

THE PROBLEM: (See figure 1) When the MP3 player is powered by the LM317
(instead of AAA battery) I hear a lot of noise; I guess it must be ripple
(?) amplified by the amplifier.
I then tried figure 2, but still there was a lot of noise.
QUESTION: does anyone of you know how I should get rid of the noise?

Thanks again!
Eibert




**My 1st Question was**: For an art project I need to build a small 1,5V
power supply to power a

small MP3 player. (replace a 1,5V AA battery)
Available is 8-10V DC. I know a little bit about electronics, enough to

build a simple schematic

 

[Costas Vlachos]

Dear all,

First of all I tried the simplest approach suggested by some of you:
. ___ Imax
. 8-10V o-------|___|------o------>-----o ~1.4V
. R |
. |
. |
. V 1N4001
. -
. |
. |
. V 1N4001
. -
. |
. |
. ===
. GND

This didn't work; the 8-10V power supply also stepped down to approx 2V. As
a result the amplifier connected to the MP3 player (and to the same power
supply) stopped working.
Next I tried the LM317 (see below & see attachment) This seemed to work as
it gave me 1,5V.

What??? The 8-10V supply went down to 2V??? What value of R did you use??? I
hope you didn't take R to mean 1 Ohm!!! I tried the above circuit in the lab
and it worked for me (gave me from 1.3V to 1.4V for a few tens of mA of
current which the MP3 player should draw). You must have done something
wrong here.

THE PROBLEM: (See figure 1) When the MP3 player is powered by the LM317
(instead of AAA battery) I hear a lot of noise; I guess it must be ripple
(?) amplified by the amplifier.
I then tried figure 2, but still there was a lot of noise.
QUESTION: does anyone of you know how I should get rid of the noise?

I can't see the binary newsgroups from here, so can't see your figures. Try
to add a capacitor at the output if there isn't one already. See the LM317
data sheet for recommendations. There is a circuit in there that has
improved ripple rejection - that may do the trick. Is your 8-10V adequately
filtered?

Hope you sort out the problem, good luck.

Costas

 

[William P.N. Smith]

This didn't work; the 8-10V power supply also stepped down to approx 2V.

Tell us more about this 8-10V supply, what is it and what's it's
current rating?

Next I tried the LM317 (see below & see attachment) This seemed to work as
it gave me 1,5V.

THE PROBLEM: (See figure 1) When the MP3 player is powered by the LM317
(instead of AAA battery) I hear a lot of noise;

When you run the amplifier off the 8-10V supply and the MP3 player off
a 1.5V battery, do you still get this noise?

Try bypass caps on the input and output of the LM317.

 

[Bob]

Try a tantalum capacitor across the output. Maybe 2 or 5 uf.