Hi,
I use COB led strip, image attached for reference off a 3.7V battery. Im wondering if its possible to have Cree led strip similar to this and if it can still run off a 3.7V battery. I`m not very conversant with the different and multiple Cree Leds that are available but perhaps someone has had an issue with this or can point me to a direction of such a LED strip made with Cree LEDS. And also would such a strip be more efficient/ brighter than using COB LED?
You’re dealing with the voltage drop across the LED strip, what we call forward voltage.
Running the led module off a single cell battery pack, your battery source I’m guessing would start around 4.2V and end up maybe 3V on the low end.
If you’re looking to go without a constant current driver and use a chunky wattage resistor you need to find an LED strip with a forward voltage below 3.7V.
You then need some amount of voltage above that Forward Voltage to drop across a resistor. To give an example, if you had an LED strip with 3.2V Forward Voltage you would subtract that from your Source Voltage
The formula to calculate what resistor you would need is
( Voltage Source - LED Forward Voltage) / LED Current
3.7V battery - 3.2V forward = 0.5V
and lets say you had a module that needed to run on 500mA
0.5V / 0.5A = 1 Ohm Resistor.
Click Here for DigiKey’s online LED Series Resistor Calculator
I’m not seeing that we have any LED strips that have that low of a forward voltage, a lot of modules will run their LEDs in series which increases the forward voltage to higher than your battery source can deliver.
You’d lose some efficiency but possibly it could work with a DC to DC Boost module like this one: DFR0952 DFRobot | Power Supplies - External/Internal (Off-Board) | DigiKey