# driving 3 LEDs (1.5A each)

Hi, I am want to use the arudino to flash 3 LEDs with (1.5 A) for a very small flash duration (a couple of milliseconds). I was wondering if any one knows of good LED drivers that can provide 1.5 A and can easily used with ardunios. It can be 1 driver for each LED or one driver for the three of them. In addition, I was wondering if arduino is capable of such a small flash duration.

note: the voltage requirement of each LED is around (3 to 4 V). Thanks

Hi, I can tell you that Arduino can time things down to microseconds (1/1000 of a millisecond). Unfortunately I can't help you much with the neccessary drivers... I'm sure someone will be along in a minute....

For the switch a logic level N channel MOSFET will do the job nicely.

To power the LED's you have the option of connecting all 3 in series with a current limiting resistor and powering from a 15V 1.5A (minimum) power supply, or the 3 in parallel each with a current limiting resistor and a 5V 4.5A (minimum) power supply. Another option (if the Flash frequency is low) is to use a large capacitor as a charge reservoir and discharge via the switch and current limit resistor (s) into the LED's.

Put a 220 Ohm resistor between the Arduino logic line and the FET gate pin to stop the switch oscillating at radio frequencies (due to poor grounding and parasitic inductance/capacitance/feedback paths).

Use micros() function for timing.

Isn't some kind of constant current driver needed for leds of this size?

The series resistor for 12V supply and leds in series would have to be (12 - 3×3.5)÷1.5=1 Ohm. A 1 Ohm series resistor does not sound like it would protect the leds very well. It would also have to dissipate 2.25W.

With 5V supply and leds in parallel, the 3 series resistors would need to be (5-3.5)÷1.5=1 Ohm, so the same problems, if I am correct.

PaulRB

A one ohm resistor would dissipate 2.25W, but as the duration of the pulse is only a few milliseconds, then the average power is likely to much lower, unless the pulses are frequent.

Just got back from a few weeks away so have had a chance to find the FET I like to use. It is a 16N03L, data sheets here. The data sheet schematics should help you figure out how to connect up.

FET has a 30V 16A switch capability in a conveniently small leaded package (TO-251AA).

Not sure if they are still available as I acquired some old stock and the data stamp is 1996!

If you provide more details about what you are trying to achieve plus LED part number and desired flash frequency then that will help select a solution. Watch out for fault/error situations that may destroy your LEDs if they are not rated for 1.5A continuous, e.g. you make a mistake in your sketch and the logic output sticks high keeping the FET on! Add a resistor on the Arduino logic output pin to ground so the FET is kept switched off when the Arduino is being reset/booting/programmed.

Don't forget some high+low frequency decoupling (say 10nF + 100nF + 1000uF) on the LED supply voltage to absorb the inductive kick back that occurs when trying to switch off a high current quickly. Minimise lead lengths in the LED+FET+R+C loop.

A 15V supply (as suggested) is a better bet for reducing the current and hence inductive kick back from parasitic inductance in the wiring. Series LED forward voltage will be in the range 9V to 12V, hence the suggestion of a 15V supply. This means somewhere between 3V and 6V across the current limit resistors, hence a "select on test" value of 2.2 to 3.9 Ohms should be fine. I suggest a minimum 5W rated resistor (or 5 off 1W (10 to 22 Ohms) in parallel). Actual dissipation will depend on the ratio of on to off time.

For ~\$5 you should just buy an appropriate driver. You'll probably want one with a "dim" input since some tend to have a bit of a lag time before they turn on if the dim is not available -- or at least you get a spec "turn on" time (350ns for the MBI6651) that you can rely on.

http://store.sure-electronics.com/led/high-power-10w-1-5a-led-dc-driver

You can find these on eBay as well.

www.ebay.com/itm/High-Power-10W-DC-input-9V-36V-1-5A-LED-Driver-buck-power-supply-PWM-DIM-/380236759063

Another solution, would be to use a LM150 with each LED. You can control it with the arduino delayMicroseconds() and the output is up to 3A from 1.2V to more than 30V.

A nice and easy use solution if you use a heat sinker.

Chagrin: You can find these on eBay as well.

www.ebay.com/itm/High-Power-10W-DC-input-9V-36V-1-5A-LED-Driver-buck-power-supply-PWM-DIM-/380236759063

At \$1.49 they look like a bargain. Normally the MBI6651 can only deliver about 800mA into 3 LEDs but it looks like 2 circuits are wired in parallel in this product to boost the current to 1.5A.

So cheap I have ordered some to play with. Thanks.

PS. I see shipping costs boost the price up!

kyrollos: I am want to use the arudino to flash 3 LEDs with (1.5 A) for a very small flash duration (a couple of milliseconds). I was wondering if any one knows of good LED drivers that can provide 1.5 A and can easily used with ardunios.

I actually did this a number of years ago to build a digital stroboscope. I never did find a suitable driver, so I ended up using a TIP31 transistor with a suitably high wattage current limiting resistor. It wasn't the most efficient solution, but it worked.

The cheap little flashlight drivers don't work fast enough for a strobe.