# How do I step down voltage and current in a DC application?

## Background

I am currently building a RC multicopter that utilizes an 11.1 V 20 C 2200 mAH LiPo battery as it's main power supply. This is fine to run the ESC's and motors; however, I also need a 5 V/2 A power source to run a PCB that is laden with an Arduino project consisting of digital sensors, GPS, LED controllers, etc.

## Question

How do I produce the proper voltage (5V) and minimum current (2 A) from the primary source (11.1 V/20 C)? Is it as simple as calculating a correct resistor value or should I do something else? I don't want to fry my sensors!

• Have a look at TLV62130 Jun 20, 2012 at 15:06
• Oops, it is 2.5MHz. Don't have a look at it, yet. Jun 20, 2012 at 15:08
• Aha! I've found a great IC for you: LM20323! Jun 20, 2012 at 15:14

Basically there are two types of voltage regulators: linear and switching. Linears are bad: if your 5 V needs 2 A it will also draw 2 A from the 11 V input, and the difference, 6 V x 2 A = 12 W, will go up in heat.

You need a switcher. Since you're going from a higher to a lower voltage that will be a buck converter. (Lower to higher voltage is called boost.) Buck converters can reach efficiencies higher than 90 %, then the power loss will be less than 1 W. Here is a selection of switchers that fit your requirements.

For maximum efficiency I would suggest that you remove the NPC1117 voltage regulator from the Arduino (I'm referring to the Uno, other Arduinos will have a similar linear regulator), and connect the output of the switcher to the 5 V net directly. Otherwise you would have to supply at least 6 V, and lose 800 mW in the NPC1117 regulator (it can supply maximum 800 mA).

Whenever possible try to run as much as possible at lower voltages, like 3.3 V. A switcher going from 11 V to 3.3 V will have a lower efficiency than one going to 5 V, but you'll gain by less dissipation in the 3.3 V devices. I even think (not checked!) that Arduino can run at 3.3 V.

• Thanks as always stevenvh! BTW--I am not actually using the Arduino itself, I have produced a PCB with the ATMega328, xtal, caps, and SPI pins so I can re-flash if necessary. So now it appears I just need a buck converter between my battery and power rails on the pcb. Thanks again! Jun 20, 2012 at 15:16
• @Matthew - The pleasure is all mine! :-) Success! Jun 20, 2012 at 15:18
• I have ordered a buck converter, but in the meantime I cannibalized an old DC cell phone charger from my car and used the tiny pcb from it to step down the LiPo voltage to a perfect 5V!! Jun 21, 2012 at 14:25
• @Matthew - Great! What converter are you gonna use? Jun 21, 2012 at 14:28
• Just this cheap one I found on ebay: cgi.ebay.com/ws/… Jun 21, 2012 at 14:35