This is the FemtoBuck, a small-size single-output constant current LED driver. Each FemtoBuck has the capability to dim a single high-power channel of LEDs from 0-350mA at up to 36V while the dimming control can be either accessed via PWM or analog signal from 0-2.5V. This board is based off of the PicoBuck LED Driver, developed in collaboration with Ethan Zonca, except instead of blending three different LEDs on three different channels the FemtoBuck controls just one.
For the FemtoBuck, we’ve increased the voltage ratings on the parts to allow the input voltage to cover the full 36V range of the AL8805 driver. Since the FemtoBuck is a constant current driver, the current drawn from the supply will drop as supply voltage rises. In general, efficiency of the FemtoBuck is around 95%, depending on the input voltage. On board each FemtoBuck you will find two inputs for both power input and dimming control pins and an area to install a 3.5mm screw terminal. Finally at either side of the board you will find small indents or “ears” which will allow you to use a zip tie to secure the wires to the board after soldering them down. This version of the FemtoBuck is equipped with a small solder jumper that can be closed with a glob of solder to double the output current from 330mA to 660mA.
If you want to get more current then 660 as described in the hookup guide the replacement resistor equation solves for this, use calculated resistor value to place one smd resistor of that value in place of the two current resistors on the board.
Do NOT solder the jumper.
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Skill Level: Rookie - The number of pins increases, and you will have to determine polarity of components and some of the components might be a bit trickier or close together. You might need solder wick or flux.
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If it requires power, you need to know how much, what all the pins do, and how to hook it up. You may need to reference datasheets, schematics, and know the ins and outs of electronics.
Skill Level: Rookie - You may be required to know a bit more about the component, such as orientation, or how to hook it up, in addition to power requirements. You will need to understand polarized components.
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Based on 14 ratings:
1 of 1 found this helpful:
Just what I was looking for, a small constant current driver for my COB and LED lights. The solder jumper allowing double the current is great, or I can simply replace the resistors and get up to 1A out of it if I so choose. Haven’t noticed any substantial heat buildup at all, so it’s a very efficient driver. Love the package size most of all since it can be fully enclosed in standards shrink tubing, and has indents for zip ties for easy attachment.
I needed a very small form-factor dimmer with which to drive some 12 volt LED tape, and this thing was just the ticket! I powered it with two 9 volt batteries wired in series. For control, I tapped into V in with a small potentiometer (Sparkfun product # 9806) and used that with a couple of resistors to make a variable voltage divider.
All in all, it worked very well for the project and gave me a tiny dimming controller suitable for embedding into a hand-held theatrical type prop. My only complaint would be that there weren’t any example circuit diagrams on how to use it with an analog voltage, but that turned out to be fairly easy to figure out on my own.
Wired this up with 5 of the 3W warm white LEDs, a switch, and a cheap 24VDC power supply from ebay. About $25 total cost, plus a couple of hours to wire and mount components with hot glue. Slipped the femotobuck into heatshrink tube. With the default 330mA drive, this provides plenty of light for under our kitchen cabinets. My wife is happy, and that’s all that really matters…
0 of 1 found this helpful:
I hacked together a prototype “hat light” last weekend, and now everyone at work wants one. Used two 18650 cells, a pair of 1 watt LEDs, the FemtoBuck LED Driver, a toggle switch, and way too much hot glue… I work as a mechanic, and spend most of my time under trucks, and got tired of holding a light with one hand, and trying to work with the other. Seemed every time I needed a light, I also needed both hands. This is the perfect solution. Super efficient, too, have gone almost a week of normal use, on the first set of batteries. That would be 3 to 4 hours per day typically. Life is good!
Cool build, and great use for this!
It’s small, it’s simple, it’s easy to hide in a piece of shrink tubing and it does exactly what it says it does. I don’t think you can ask for more than that.
I used it to power some of the 3W warm LEDs from a solar battery source for a long camping trip. Worked very well!
I have used the Femtobuck on multiple projects. Primarily I use them with my robotics team to drive LEDs that illuminate Vision targets. The true advantage to the Femtobuck is that it provides a constant light output from the LED regardless of the battery voltage. Additionally, with the dimming control input, you can vary the output as needed. The physical layout of the board also makes it very simple to secure wiring with zip ties to the board. It would be nice if these were available in 10 packs.
Using 2 to drive Luxeon Rebel Stars as the landing lights on a giant-scale RC airplane. Using the 350mA option (open jumper) and a 2S LiFePO4 as the power source. Everything wired inline and covered with shrink. Wiring was easy and the LEDs are painfully bright.
The landing lights are simple on/off so I didn’t get to use the onboard dimming bits.
For my application I required 25 mA so I removed the two 0.3 resistors and threw in a 10 that I had lying around. Worked exactly as expected. Very nice and compact.
The FemtoBuck is quite small, but easy to wire. I used a 10K pot for the control and it is perfect for the 3W LEDs.
NOTE: My FemtoBuck is in a tight space over a ProTrinket. When I operate the 3W LED the my RGB light strip flickers. It is not a problem for me since I will never operate both at the same time. I could move or shield the FemtoBuck to fix the issue.
This works as advertised. My only request would be that it have additional resistors to allow current values up to the maximum that the driver can handle, which I think is 1 Amp. 600mA max is OK for proof of concept, but I need to drive my LED harder, so I’ll be making my own board with higher current capability.
Great little led drives, no complaints
I have some of the SparkFun 3W LEDS, and I’m using this to drive them for a sign. It works great, and is easy + reliable!
Using it for computer controlled house LED downlights.