thank you, jake. i think have all the parts - just need to pull the inductor, resistor & cap. my plan is to make a pan/tilt/focusable spotlight controlled by dmx :)

On Sat, Jun 20, 2015 at 7:20 PM, Jake <jake@spaz.org> wrote:
put two 19v laptop adaptors in series with an n-channel mosfet, and have an arduino powered by only the lower 19V adaptor which controls the mosfet.

put an inductor between the transistor and the LED -, and also put a diode from the inductor (where it connects to the drain of the mosfet) to the + of the LED, where it's connected to the + of the upper 19v laptop adaptor.
put a good capacitor in parallel with the LED, rated for like 50 volts or more.

in the arduino, set the PWM frequency to the highest it will go - a divisor of 1 will yield 31 or 62 kHz depending on which pin you use.

connect a knob to one of the analog inputs, and write a program that reads the value of the knob and sets the PWM accordingly - although make the software limit the maximum PWM according to what you determine is the max power the light can handle.

keep the transistor and LED cool.  Remember that the heatsink of the transistor must not electrically contact anything else - it is the drain (middle pin) electrically.

of course you can write programs to control the brightness from patterns you create, instead of just looking at the knob.  Or you can make an audio input to one of the analog pins control brightness.  As for controlling servos, you can control 2 servos with an arduino pretty easily, on pins 9 and 10, it's one of the examples that comes with the arduino IDE.

as for the fan, just connect it to one of the 19v power supplies with a series resistor so it gets the right amount of power.  If it's a 1w 12v fan, you will need a resistor like around 84 ohms, dissipating 0.58 watts. A 100 ohm 1w resistor would be fine, or a 50 ohm resistor if you want the fan to blow faster.

-jake

On Fri, 19 Jun 2015, Robert Benson wrote:

I'm trying to drive several devices:

1) 1x 1w 12v fan (pentium 2 cpu cooler)
2) 1x 100w 35v 3a smd led. (I want the led to be dimmable & ideally capable of high
frequency switching :))
  *  Forward Voltage (VF): DC 32-34V
 *  Forward current (IF): 3000MA
 *  Out put Lumens: 8000-9500LM
3) several other servo/stepper motors for pan/tilt type uses

with one arduino uno.

Obviously, the arduino will not power the led so I need a driver for it & maybe even the
motors.

My research leads me to think that the led wants a constant current of 3 amps & a variable
voltage for dimming. Circuits of this caliber have not been forthcoming in my searches on
the web.

Thank you for your consideration. Cheers
Robb