# Building a drone strobe with Cree XP-E2

#### ilium007

Joined Aug 24, 2013
128
Hi - I am looking to build a strobe for my Mavic Pro using a Cree XP-E2 LED (Cree XP-E2). I have got the LiPo charge / LVCO circuit figured out using a the standard TP4056 / DW01 / FS8205A combo. I am going to sequence the strobe using a simple ATTiny45 / NPN MOSFET. I am not sure if a simple current limiting resistor will suffice or if I need to look at a constant current circuit to drive the LED.

LED will double flash 50 ms on – 60 ms off – 50 ms on.

I am going to run a 1S / single cell 3.7V 70mAh LiPo such as this one - https://www.aliexpress.com/item/32509826953.html

I will probably drive the LED at 700mA as per the datasheet:
https://www.cree.com/led-components/media/documents/XLampXPE2.pdf

If I should run a CC circuit, Is there a specific IC I should be looking at?

I have found the CN5711 - I could simply pulse the CE pic and do away with the MOSFET.

Operating Voltage Range: 2.8V to 6V
On-chip Power MOSFET
Low Dropout Voltage: 0.37V @ 1.5A
LED Current up to 1.5A

Thanks!

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#### ilium007

Joined Aug 24, 2013
128
This common one also seems to make things very simple - AMC7135

Two in parallel for approx 700mA. I could drive VDD directly from the ATTiny.

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#### LesJones

Joined Jan 8, 2017
3,110
As your LED requires about 2.9 volts and your supply voltage will vary from about 4.2 volts down to about 3.3 volts controlling the LED current will be difficult. If you chose a resistor to limit the current to 1 amp when the battery has just been charged (Say 4.2 volts.) you would have a 1.3 ohm resistor. when the battery was down to 3.3 volts the current would be 0.4/1.3 = 0.307 amps. Making a constant current circuit that will work with as little as 0.4 volts across the current sense resistor and control device (Probably a mosfet.) would also be difficult.

Les.

Joined Feb 20, 2016
3,796
If you can use a greater than 6V supply, these might be good. I have just ordered some to have a play with.
https://www.mornsun-power.com/uploads/pdf/KC24JT-xxxR3.pdfThe version I am looking at is the KC24JT-700R3 as it has 700mA current, 6 to 36Vin. Analog and PWM dimming. Price under \$5.00 so they sound like a good device to me.
If I remember, I'll report back if anyone is interested, but they are at least 3 weeks away.

#### ilium007

Joined Aug 24, 2013
128
I really need to stick with 1S due to the complexities of balance charging more than 1 LiPo cell. I can buy these tiny LiPo cells easily and need to keep it all small because 4 of them are going on my DJI Mavic Pro drone.

I could possibly find another bright Cree LED with a lower forward voltage drop. All the reserach I have done comes back to a lot of flashlight manufacturers using the AMC7135 with single cell LiPo / Lion 4.2V batteries.

#### ilium007

Joined Aug 24, 2013
128

This is an example of the AMC7135 driving a high power LED torch from a single 18650 Lion cell.

#### eetech00

Joined Jun 8, 2013
2,302
Hello,

I have a MAV Pro also....

I'd use a PWM driver to go easy on the batteries. The current regulator will provide a continuous constant current.
I realize the strobe will be flashing, but a PWM will control the duty cycle so as not drive the LED with 100% current all the time.

"LED will double flash 50 ms on – 60 ms off – 50 ms on."

Milliseconds? You wont be able to see the flash...?

eT

#### Wolframore

Joined Jan 21, 2019
2,245
Driving 700 mA using 70 mAH battery with current for the tiny. How long will it last.. are you running 4 of them? Same battery? Also are they all on at same time? Almost 3 amps? Just unclear on your requirements.

#### ilium007

Joined Aug 24, 2013
128
Driving 700 mA using 70 mAH battery with current for the tiny. How long will it last.. are you running 4 of them? Same battery? Also are they all on at same time? Almost 3 amps? Just unclear on your requirements.
1 LED / 1 1S LIPO

#### ilium007

Joined Aug 24, 2013
128
Hello,

I have a MAV Pro also....

I'd use a PWM driver to go easy on the batteries. The current regulator will provide a continuous constant current.
I realize the strobe will be flashing, but a PWM will control the duty cycle so as not drive the LED with 100% current all the time.

"LED will double flash 50 ms on – 60 ms off – 50 ms on."

Milliseconds? You wont be able to see the flash...?

eT
I chose those times based on an Airbus A320 strobe part so I'm pretty sure it will work but obviousy that a minor point that can be easily fixed in code.

#### eetech00

Joined Jun 8, 2013
2,302
I chose those times based on an Airbus A320 strobe part so I'm pretty sure it will work but obviousy that a minor point that can be easily fixed in code.

View attachment 193710
Oh..ok...so that's not the flash rate.
The flash rate is 60 flashes per minute.

eT