use Arduino's on chip ADC to measure current?

[ice595]

I want to use an Arduino to control 3 high power LED chips. Each LED chip can take 10 watts.
im using a mosfet switching circuit with PWM to drive those LEDs.
From what I have heard, high power LED chips require a current source to driven properly.
Is there a easy way to sense DC current with the ADCs on the Arduino.
I wouldn't think its as easy as using a current sense resistor in series with the LED and use the ADC to measure voltage across the resistor then use ohm's law. Since the LEDs are driven by PWM rather than a smooth analog voltage.

Any ideas on making this happen?

[idpromnut]

I'm a bit of a noob myself, but I would think you would build a CC driver, and then PWM the driver, thus removing the need to sense the current (since it would be guaranteed to be constant anyways). After that, I don't know why you would want to measure the current, except to calculate actual power usage or something of that nature?

[theatrus]

Is your current design just a PWM to a FET in order to turn on and off the LED? What, if anything, are you using for current control?

For something in the multi-watt range, you probably want to use a standard buck (or boost) topology, which means you are controlling your PWM circuit based on current through the string and the current in the inductor. While a linear CC driver is possible, your efficiency is pretty terrible unless you can very closely match the input voltage to the needed LED voltage (+offset).

You can save yourself a lot of heartache (and broken LEDs) if you use an existing buck controller, which are quite cheap these days. An NCP3066 is a cheap option, and has a built-in PWM control input. Depending on how the LED chip is made (series, parallel), the LM3404 (HV) can also drive high voltage 1A series strings.