Interfacing and controlling a high brightness LED to a microcontroller

[melillo]

I have to build a device where a circuit will flash a high brightness white LED. The flash frequency and intensity will be controlled by a PIC microcontroller. The frequency will vary from 1 to 12 Hz and the intensity will be controlled using PWM. The microcontroller part is not a problem: one of the PIC pin is toggled on and off at a low frequency, and the PWM signal (5KHz, variable duty cycle) is sent to another pin. These two pins are connected to the inputs of an AND gate, the output of the gate controlling the LED. I need some advices about choosing and connecting the right LED, the right LED driver and the right power supply.

The LED intensity must be in the 150 to 200 lumen range.

I have found this LED: http://www.digikey.ca/product-detail/en/L2-TGN1-F/492-1671-ND/3694225

141 lumen at 200mA, input voltage 5.2~5.3V. It is supposed to include the driver circuitry, although I haven’t seen it in the datasheet. Can I just use a 6V voltage regulator (MC7806CT), thru a transistor driven by the AND gate and connected directly to this LED? Also, do I have to use some sort of heatsink?

I also consider this LED: http://www.digikey.ca/product-detail/en/A008-EW830-Q2/788-1044-ND/2720735

In this case, what should I use for driver, power supply and heatsink? What’s the best way to connect it to my AND gate?

By the way, I have this driver right now: http://www.jameco.com/webapp/wcs/stores/servlet/Product_10001_10001_2156287_-1 Can it be useful?

I’d really appreciate some hints.
Thank you in advance and have a nice day.

Marc

 

[Arouse1973]

This might work, just put this together for you to have a look at. It is a constant current LED source. You may have to adjust the 4R for different currents. With the 4R and the other components it gives you 160mA. Make sure you drive the input with a nice fast rising edge and you might be better with a logic level N-FET. You need to choose an FET with a low RDS on of say less that 50mOhm and current rating of say 2 Amps or above. Just giving you some idea.
Thanks
Adam

 

[melillo]

Thank you Adam for your answer, I appreciate. I suppose that in your solution, you refer to the first LED (Bivar). The specs for this LED are:
160 lumens at 350 mA (ok for me), Vf = 5.2 V, Input voltage: 5.6V. I don't understand that last value. I suppose that this is the voltage that must be applied to the LED so that it's internal driver works correctly?

You say that with your solution, a current of 160 mA is generated. Isn't it too low for that LED? And how do you get this value, considering that the voltage drop across the LED is equal to your voltage source?

Finally, should I use a driver (current regulator) with the second LED (LuxDrive) I mentionned?

Thank you!

Marc

 

[(*steve*)]

You should use a constant current source for *any* high power LED.

As Arouse has said, you adjust the resistor to set the current.

The current (in Amps) is approximately 0.65/R (R in ohms)

If you want 350mA, then R = 0.65/0.35 = 1.86 ohms. The easiest way to get this is to place two 3.7 ohm resistors in parallel. A closer value can be obtained by placing a 12 ohm resistor in parallel with a 2.2 ohm resistor. A 1.8 ohm resistor may also be close enough.