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: https://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: https://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

 

[BradtheRad]

Starting from your transistor idea:

R2 is good to include because it reduces the risk of exposing the LED to overcurrent.
(Another way to reduce LED current is by increasing bias resistance R1. This tactic requires careful measuring and adjusting.)

The supply V is not critical. I chose 9V because it is enough to do the job, and to show how R2 serves to drop voltage and dissipate power. (You mention a regulator IC however R2 does a similar job.)

The LED uses 1 W of power. If it were lit all the time, it might heat up enough that you should use a heat sink. However if the duty cycle is low, then you will not need a heatsink.

 

[betwixt]

That's the complicated way. Use the transistor a Bradthe Rad suggests and use a PWM output from the PIC but forget the AND gate, just enable or disable the PWM output to turn it on and off.
It will work better if you can use a logic level MOSFET instead of a bipolar transistor. I control lighting using PWM from a PIC through a 2SK2989 MOSFET which is happy with 5V gate drive but these are now obsolete, any similar device with low Vgs threshold should work.

Brian.

 

[melillo]

Thank you Brian and BradtheRad for your answers, I appreciate. Ok, I will use a MOSFET, that's a good idea. Here are the specs for the first LED I mentionned in my first post:
160 lumens at 350 mA
Vf = 5.2~5.3 V
Low input voltage (5.6VDC)

For the light intensity, I may have to increase the current a bit to get more intensity. I won't exagerate, because I'd like to not use a heatsink because the place where I need to put the LED is rather small. Also, I don't know what the last spec (input voltage) means. Is it the voltage needed across the LED so that's its internal driver works correctly? (It says on the Digikey site that it has an internal driver, but it is not stated in the specs).

And if I go with the second LED (Luxdrive), should I use a driver (constant current) instead of a resistor?

Thanks a lot!

Marc

 

[BradtheRad]

A mosfet is suitable to drive it. (My simulation shows a transistor because the current flows make it easy to observe expected behavior.)

Also, I don't know what the last spec (input voltage) means. Is it the voltage needed across the LED so that's its internal driver works correctly? (It says on the Digikey site that it has an internal driver, but it is not stated in the specs).

Yes, the figure for input voltage is the minimum supply V. I guess a it has a regulator which limits current to a safe level.

However since you want to flash the led rapidly, you probably want total control over it. A built-in onboard driver could get in the way somehow.

So if you take total control, then you must determine the safe level of current you can send through it. It will be tempting for you to increase current, so the led will appear brighter during brief flashes.