Transistor to communicate PWM to Buckpuck LED driv

Hello! My first post here.

I have built a DIY LED lighting rig that uses 12 buckpucks, each with ~24v @ 700ma of LEDs running on them.

I have achieved rudimentary dimming using the 0-5v analog output from a controller that I already have set up. This was achieved by getting voltage as close to 0-5 as possible in software (0.08v -4.96v), and then connecting the 0-5v signal to the Buckpuck CTRL wire, and the GND from the 0-5v interface connects to the LED (-) wire.

The only problem I have with this setup is precision. The puckpuck is also inverted, so 5v = full dim, 0v = max illumination.

When I get to around 4v, the LEDs just shut off, and they are still pretty bright before this point. not quite the 0-100% I was hoping for. I'm thinking its because the 0-5v signal isn't very good, or is perhaps based on a low hz PWM signal to start with??

I was thinking as a solution to use an Arduino, take that existing 0-5v input, invert it, and map it to a set of PWM values.

From here there are two ways to go (that I know of!)

1) I can connect the 0-5v PWM signal from the Arduino directly to the CTRL line from the buckpucks and common the LED (-) to the arduino ground.

I've read some posts here saying this isn't the most efficient, since the LEDs are never pure ON, they will always be running a duty cycle even with it set to max. What kind of efficiency loss can I expect with this method?? Will it reduce the life of my components?

I favor this method for ease of installation :)

2) Use a MOSFET transistor where the arduino connects to the Gate, and the source/drain connect to the power supply and LED (-). The IRF510 would work nicely for this.

Method #2 is probably more robust and will drive the LEDs better, but I would need one MOSFET for each BUCKPUCK, really complicating the wiring job.

Is there another option??? Is it possible for me to convert the 0-5v PWM signal back to a 0-5v analog control for direct current control of the buckpucks?? And if so, would it be smoother/better in the low range than the crappy 0-5v signal I already have to deal with???

My main concern is I want very smooth dimming from OFF to barely ON. Maybe this is just not doable with the buckpucks?

Really appreciate any ideas people can provide. Especially if you think RAW PWM on the puck will be just fine without affecting output too much :)

bumpity :)

Your problem is with feeding a PWM signal into something that expects an analog signal between 0-5v. You need to filter the PWM signal with a low pass filter.

Off the top of my head - try a 6.8k resistor and 0.47uF cap

Or try reading:- http://www.thebox.myzen.co.uk/Tutorial/PWM.html

To which I owe a lot :)