1.5 volts power supply from a Car

[Bill Briand]

Hi All,

I just bought a car indoor/outdoor thermometer and it requires 1.5 v
DC to operate. I am installing it into my car and I would like to
have its power supplied from the car battery.

I took apart the device and there is a transformer mounted inside. I
may try to figure out its input and output voltages but I wanted to
post this first to see what building a 12-18 volt to 1.5 volt
regulator would entail.

I see a lot of posting for LM317 (or was it LM376??). Would this do
the trick. Will the output voltage vary much if the input voltage
moves between 12-18 volts?

Thanks for any suggestion on the best way to do this.

Bill Briand

[Xenos]

If it uses 1,5V then it is using a battery. I have not seen a device running
on 1,5V that has a transformer. Are you sure you can tell a transformer?

"Bill Briand" <bill_...@hotmail.com> wrote in message
news:674c672d.02021...@posting.google.com...

[Daddio683]

<< I wanted to
post this first to see what building a 12-18 volt to 1.5 volt
regulator would entail.>>

Bill,
An LM317 regulator should do you just fine.
Place a 240 ohm resistor from the Vout terminal to the Adj. terminal and a 51
ohm resistor to from the Adj. terminal to the Battery neg. (12V- or Gnd). This
will give you 1.5 Volts between Vout and 12V- for any input voltage (Vin to
12V-) from about 4 to 40 Volts. Except for a small capacitor at the input and
output, thats about all the parts you need.
For more information go to:

www.national.com
and
www.onsemi.com

and lookup the data sheet for the LM317.

Regards,
Gary.
Don't send me nojunk in my email!

[Bill Briand]

Seriously there is a transformer under the hood - so to speak. I
bought it from Canadian Tire (it is the $17.99 model). I don't know
how much voltage it outputs (if its either more or less than 1.5
volts).

Now I am wondering if its more than 1.5 volts how harmfull would it be
to remove the transformer and just regulate the LM317 to what the
output of the transformer is? Or should I just use the LM317 to just
do the 1.5?

Thanks again for yours and Gary's replies!

Bill Briand

"Xenos" <xenos_...@hotmail-nospa.com> wrote in message news:<a4panf$6a$1...@usenet.otenet.gr>...

[Gary Lecomte]

dadd...@aol.comnojunk (Daddio683) wrote in message news:<20020217193019...@mb-mr.aol.com>...

**************************************************************************
Instead of the normal LM317, use a LM317LZ. It's much smaller in a
TO-92 package and will handle 100 Ma.

Gary

[Xenos]

In the 12V of the car, (input of LM317) add at least one 220nF/63V as a
filter for the noisy power supply of a car.
You should consider that an LM317 is not very fast in input voltage changes
(if you see datasheets you can see that some sparks could pass thru to your
device!).
Use 220nF/25V parallel to the 1,5V output to add some more filterring.
A small ferrite ring would be helpfull in the 12V line also (do a few turns
in it).

"Daddio683" <dadd...@aol.comnojunk> wrote in message
news:20020217193019...@mb-mr.aol.com...