Most Efficient way 12V DC to 3.7V DC

[trackerman]

Hi all
I've an alarm unit that's powered by a standard 3.7V DC mobile phone battery.
I want to use a 12V battery pack to extend the life of the alarm unit.
What's the easiest way to convert the 12V supply to 3.7V supply for the alarm.
I could use the standard cigarrette lighter plug ins for USB power conversion, but I imagine there would be alot of energy wasted in doing this. Am I correct in saying this?? If someone has a solution to my problem, it would be a great help

Thanks

 

[lockman_akim]

i think u should use voltage regulator or use voltage divider theory..

 

[srizbf]

a switching regulator will do the work.
can get from lineartech/analogdevices/national etc.
a single chip solution is available .

 

[lockman_akim]

switching regulator? can u tell me a little bit..

 

[srizbf]

please see:
**broken link removed**

and

http://en.wikipedia.org/wiki/Voltage_regulator

to understand if you are new to it.

 

[karesz]

Hi,
National Semiconductors web side: "simple switcher" ie., but such other vendors as PI, LT(linear Technology, TI, ST, Micrel, On Semi...
Simplest simple switcher are maybe the easiest to design_online:
**broken link removed**
But other producers have good tools "PI Expert Design Software" too: PI (Power Integration): **broken link removed**
K.

 

[Slammer]

Use MC34063.
https://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF

Most DC converters for mobiles use this chip (is the cheaper switcher).

You need 3 resistors, 2 caps, one diode and one inductor.

 

[karesz]

Hi Slammer,
Nice thing, but efficiency of ca. 62% isnt a peak & it will be not compensated w. some better price ($ 0.80... 0.90) if you have a battery often to change :-(
K.

Added after 5 minutes:
Hi Trackerman,
USB isnt supplyed (as I know) at 3.7V: http://www.datatranslation.com/phpkb/question.php?ID=235
"What is the specified USB port supply voltage range?
The High Power USB port must be between 4.75 and 5.25 volts. The Econ modules have been tested from 4.65 to 5.5 volts without any problem. The DT9812 series will usually use less then 400mA of the 500mA current specification. *Created: 12/20/04"
K.

 

[smeezekitty]

**broken link removed**