Deploy a homemade strobe system using Cree 10W LEDs

[lingyueqing]

I've deployed a homemade strobe system using Cree 10W LEDs in my homebuilt aircraft. My implementation uses a simple PIC controller to do the flashing, an IRL2505 mosfet (driven by an NPN transistor) for the switching, and a linear regulator (LM338T: LM338T - NS - PMIC - Voltage Regulators - Linear - Kynix Semiconductor) to limit the current to 5 amps. The system is using 7 Cree's in parallel for the landing light, and 8 in parallel for each wing strobe unit, each driven by an independent IRL2505/LM338 5 amp drive circuit.

 

Details can be found in this instructable:

 

LED Landing Light for Experimental Aircraft

 

After adding a protection diode to manage inductive field collapse on the wing mounted strobes, the system is working fine... however, more brightness is always better!

 

Here's the schematic:

 

So, my specific question is this... to make this brighter, I need to go beyond 5 amps. What options are there for a more efficient, higher output, physically small current regulator?

 

Some implementation constraints:

 

• There is little to no space in the wingtips or nose for the electronics, and heat is also an issue... I can't afford to have something melting my wings! I've had to work hard to control the heat from the LEDs and also from the linear regulator/mosfet. So... space and heat are my enemies...!
   
   
   
  
• Switching regulators may be the right option, but I've been reluctant to try designing one because by reputation they are inherently electrically noisy... I depend on my HF radios, GPS, bluetooth and Wifi (all currently in the airplane) - so adding electrical noise could be an issue.
   
   
   
  
• Commercial LED based strobe systems for homebuilt aircraft are out there... and I've looked at them closely. I don't see current limiters. At all. And, they are plenty bright. What gives??? What don't I understand??? Are they just keeping the duty cycle so low that the LEDs can't overheat?
   
   
   
  

 

 

 

ANY thoughts, suggestions, comments, or ideas would be welcome.

 

Thanks!

 

 

 

[scsirob]

Well done! Great project you have there.

 

A couple of years ago I modified a set of Kuntzleman position lights to include LED strobe lights. One side with a Bridgelux BXRA-N0802 LED, the other side with an array of smaller Cree XLamp MX6 LEDs. Rather than trying to regulate the current, I placed the Cree LEDs in series to have a string with nominal Vfwd of ~13.5V. Came out at 4 LEDs. Rather than try to regulate, I used a low ohm resistor in series. If you look at the Vfwd curve and Ifwd curve of the LEDs, you see it rises sharply once they reach normal working area. Say normal bus is 14.4V. For 1A of current and 13.5V Vfwd, you'd need to lose 0.9V across the resistor. A one Ohm resistor will take care of that. When bus power goes up to 15V, you'd see that the resistor absorbs up most of the current rise and Vfwd stays pretty close to normal. When bus voltage sags to below ~12V then the LEDs don't work anymore, but you'd have a different problem anyway..

 

In my application as strobe, duty cycle is low, and a bit of overcurrent isn't an issue. In fact I used a bit thinner AWG#22 wire to power the strobes in the wing tips and relied on the resistance of the long wires to limit the current ;) Perhaps you need to be more careful when running 100% duty cycle landing lights.

 

Below is the circuit I designed. I (ab)used the white LED in the position light to provide a ~3.5V power to an ATTiny microcontroller (same as your PIC chip). I didn't design a PCB, I built it 'dead bug style' inside the position lights. Has served me well for the past 5 years.

 

 

 

[Ayecapt]

One solution is to put your leds in series and raise the supply voltage by using a current limited boost converter.

 

The duty cycle will be short, remember that the retentivity of the eye is quite long . Which means short very bright pulses are easily seen.

 

Take a look at this design LED Lighting - Experimental Avionics Its not dissimilar to yours but it does use a ready made boost converter. Strobe controlers are prone to causing rf noise led units are better but still screen it and locate it carefully . Also use a rf choke capable of carrying the lamp load at the controllers power inlet.. have fun....