Any driver that could step down 7.4V to 3.2-3.8V?

FNinjaP90

Enlightened
Joined
Jan 8, 2003
Messages
888
As the topic suggests. I would like to use two 3.7V PILA 300S batteries end to end to power a 3.2-3.8V 2A laser module, but instead of running them in parallel, it would be easier to run them in series but with a regulated step down circuit. Is there any driver that could do this?
 

LEDninja

Flashlight Enthusiast
Joined
Jun 15, 2005
Messages
4,896
Location
Hamilton Canada

thehappyman

Newly Enlightened
Joined
Jul 9, 2006
Messages
189
FNinjaP90 said:
As the topic suggests. I would like to use two 3.7V PILA 300S batteries end to end to power a 3.2-3.8V 2A laser module, but instead of running them in parallel, it would be easier to run them in series but with a regulated step down circuit. Is there any driver that could do this?

Fist of all, if use use the batteries in "series" you will limit the availble current, to the laser module, to half of what would be available if the batteries are wired in "parellel".

But if you want the batteries in series, here is an easy, cheapo way to do it.
Measure how much current the array draws, and divide that into the voltage you want to "drop".
In this case you want to drop about 4 volts from the 7.4, leaving 3.4 for the laser module. For example, if the laser module draws 1 amp, Using ohms law (R =E/I) you get 4 volts/1 amp, = 4 ohms. So, putting a 4 ohm resistor in series with the battery and laser module will work for you. And you will need a 5 Watt resistor (P = I x E or 1 x 4 = 4 Watts) to dissapate the heat.

El cheapo yes, will it work, yes, but it isnt super regulated.
But you dont need that.
 

2xTrinity

Flashlight Enthusiast
Joined
Dec 10, 2006
Messages
2,386
Location
California
Are these PILA batteries CR123 sized? If so, you could just buy a 17670, which will give you a bit more energy than 2 CR123 in parallel. However, the advantage of two in series a regulated stepdown is that the brightness won't start to diminish if the battery voltage goes below 3.7 volts on each of your cells (if you have a buck circuit, and input supply voltage drops below output voltage it direct drives -- this will never happen with two cells). Note you lose this advantage if you use the "big 5 ohm resistor" method.
 

thehappyman

Newly Enlightened
Joined
Jul 9, 2006
Messages
189
The Only advantage to the resistor method is that its just one cheap, small component.
 
Top