# 120 House Current Volts down to 1.5 volts How?

Discussion in 'Electronic Basics' started by Rob \ the nut \, Jun 7, 2004.

1. ### Rob \ the nut \Guest

Hi

I would like to build a power inverter that converts 120v out of the
wall jack into 1 1.5 volts needed for a portable mp3 player ( that
will be connected 24/7 to a answering system ( hold music )

Any schematics ? is it even possible?

sorry about the newbie question, I am just wondering if its possible
since I have not see a singler power adaper that will go downto 1.45
volts

2. ### Rheilly PhoullGuest

I assume you are talking DC here, one thing you could try is to get an
adaptor that outputs 5v DC and then add a string of diodes in series with
one lead to the player. That will give about 3.5v drop across the diodes
leaving 1.5v for the player. This is better than a resistor since the volt
drop stays much the same until the current goes up beyonf that which the
player will use.

Dear Friend

Are you going to built that on your own , or you are looking for a
In case you will built it on your own , there a lot of sources to look
for.
This keyword will give you a lot web sites ....
the main idea is to define the power requirements of your device (how
many Watts or mWatts )
after that you will absolutely need a transformer .
a transofermer of 120 V Ac to 3 V AC , rated at 1 Watt , will not cost
more than 10 USD , and i'm sure that you can find one at any local
electronics components store.
After the tranformer you have to rectify the 3 Volt AC current to DC .
After that you will just need to use a Voltage regulator (i.e 7805 is
a Voltage regulator providing 5 V dc always stable , view datasheet on

I hope that you have got the basic idea , with a little bit of
searching , you will easily find out the solution.

Regards

George Vasiliou

4. ### Byron A JeffGuest

-Hi
-
-I would like to build a power inverter that converts 120v out of the
-wall jack into 1 1.5 volts needed for a portable mp3 player ( that
-will be connected 24/7 to a answering system ( hold music )

-
-
-Any schematics ?

I'm sure. but I'll simplify it in a minute.

- is it even possible?

Of course.

-
-sorry about the newbie question, I am just wondering if its possible
-since I have not see a singler power adaper that will go downto 1.45
-volts

There usually isn't much need.

You need 3 components:

1) A standard wall wart power supply, the lower the voltage the better.
6V should be trivial to find, and 4.5V should be possible to scounge up.
The local GoodWill here sells them for a dollar each.

2) A voltage regulator. The part you want is called an LM317. You can get it
for \$2 at the local Radio Shack in the parts drawer. It's job is to drop the
voltage of the wall wart to the 1.5V you require. Here's a pretty good page
on the part:

http://www.circuit-innovations.co.uk/LM317.html

The only question here is whether or not you really need 1.5V. If it functions
with 1.25V then the job is trivial: hook the Vin to the wall wart, Vout to
the player, and ground the ADJ pin. All finished except for the smoothing
capacitors (check the data sheet for more info). If you really need the 1.5V
then you'll also need to by a small value resistor (220 ohms is popular) for
the R1 described in the circuit and a small value pot (500 ohms or less)

3) Cables to connect to the target.

Hope this helps,

BAJ

5. ### CFoley1064Guest

Subject: 120 House Current Volts down to 1.5 volts How?
This Radio Shack adapter has a switch that will allow you to go down to 1.5VDC
at up to 300 mA, which should do OK for battery replacement. Make sure you
have the polarity right, or the MP3 player won't like it.

Catalog #: 273-1662 Model: 273-1662
CTLG%5F009%5F001%5F001%5F002&product%5Fid=273%2D1662

1-800-THE-SHACK (1-800-843-7422)

Good luck
Chris

6. ### Watson A.Name - \Watt Sun, the Dark Remover\Guest

Diodes won't give very good regulation. Just use an LM317 from Radio
Shaft.

Put two 470 ohm resistors from the output terminal to the adjust
terminal. Put a 47 ohm resistor from the adjust terminal to ground. If
you want it to be adjustable, instead of a 47 ohm, use a pot; if it's
100 ohms you should be able to adjust the output up to about 2V.

7. ### Robert C MonsenGuest

Of course, you mean for this circuit to regulate the OUTPUT of the 5V
wall wart, not the AC mains.

8. ### Rob \ the nut \Guest

thanks guys!!!!!!!!11