Lipo charger and 3.3v output

Hello, I have an ADA 1000 booster charger with an output voltage of 5v. I am using it as a Lipo charger and driver for a Cree Led. At that voltage and for the lumen output i want i need to include a 3ohm 5w resistor in the circuit and find that is getting a bit warmer than i want for the project i am working on.
If i run the led at 3.3v i only need a 1ohm 1w resistor for the required lumen output and that stays quite cool so i am hoping there may be a board similar to the ada powerboost 1000 but with only 3.3v output.
If anyone knows of a board that would achieve the 3.3 v output and also charge a lipo battery from a usb connection please let me know i will be very grateful.

Hi Leslie,

Best I could find is this 3.3V/5V booster by SparkFun:

Unfortunately it doesn’t feature charging, so you’d have to use a separate board for that.

I’ll keep looking but I’d say this would be the closest we have

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Hi Leslie
What is the forward voltage drop of the LED and what sort of current are you using. The board James linked will only provide 200mA @ 3.3V which I feel may not be enough for your LED.

How warm is “a bit warmer than I want”. Usually if you can put your finger on it it aint half hot yet. If you have it enclosed that may be a problem.
Have you considered a LED driver. These are constant current devices that accept a wide range of input voltages. Core have one which may be suitable SKU: COM-13716. This has a PWM input for dimming control but connecting the control point to 5V should be full brightness or I think 350mA. I think some of these devices are 350mA or 700mA selectable
Cheers Bob

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Hello Robert, Vf is 2.87v and current is 650mA. A bit too hot is just that it is running at around 50-55c and while that is ok in normal situations this complete assembly will be inside a 3d PLA printed enclosure with no ventilation so there will be some heat buildup. At 3.3v and a 1ohm 1w resistor the resistor temp is about the same as ambient so just a bit more desirable and the lumen output is around the 250l so ok for my purposes.
I am thinking a buck converter will work as a driver as really a driver as i understand it only provides a constant voltage output even when the input may vary and most of the buck/boosters i have looked at provide the same voltage regulation as a driver…I think!

Currntly i am using an ADA4920 3.3v output connected to a lipo 3.7v battery and also an Adafruit lipo charger. By setting up the circuit properly i get the led running off the Lipo if the charger is not connected via usb to a powersource and running off the PS if it is connected. It all seems to work ok but just a bit cumbersome compared to the Ada 1000 powerboost but maybe i just live with it.

Thank you again for your comments and good advice.

Hi Leslie
A Buck converter does provide a constant voltage output over a wide input range BUT the input V must be above the output V by a definite amount. Not sure what that is but probably about 1V or a bit more. Gives the “buck” process a bit of elbow room.
In contrast a LED driver will provide a CONSTANT CURRENT over a wide input range up to somewhere close to 40V in some cases. Useful if you have a few of these high output LEDs in series. In your case 10 of your LEDs would require an input voltage a couple of volts above 29V minimum. I think common preselected currents are 350mA and 700mA, sometimes selectable. I haven’t used one so am not absolutely sure.
I can see where you need to keep heat generation to a minimum and anything you can do to achieve this is OK. What about your LED?? Does that generate much heat or is his more or less open to the outside air.
Cheers Bob

Very good information thank you Bob.
The LED is in the open and is mounted on a small copper pcb so what little heat is generated is dissipated easily. I will locate the led details and post them in case you have any thoughts on its use.
Essentially it will provide the light source for a small table lamp i am designing as a result of a request from my daughter for a small portable lamp that can include a lampshade made from the block printed fabrics my daughter designs and prints and markets online.
Were i clever enough i would have a circuit on a pcb that provides the essential electronics of lipo charger, voltage control, led driver and USB connector for charging but that is way beyond my capabilities. So instead i am using breakout boards to do the job-or at least trying to. I have designed the base in fusion 360 and 3d printed it in PLA, those parts i can do very easily its just the electronics i am very slow on but what an enjoyable journey. I am hoping for this very basic prototype the breakout boards i am using will at least get the lamp, and its its brothers and sisters, operating and functioning as intended then i can address a more sophisticated electronics setup.

I have added a photo of
Cree XPG-3 on 20mm Copper TPAD Star MCPCB

A good start. Keep on with the journey. Post a pix of the finished product and be proud of it.
Cheers Bob