Hey Jean, how are you?

I have made something similar during my summer internship @ UBC Vancouver (Canada); what is have done is exactly this: http://electronics.stackexchange.com/questions/129609/how-does-this-constant-current-sink-actually-work 

and it worked pretty well for DC references but not so well for frequencies of more than some hundreds of hertz (due to low gain opamps and high mosfet capacitances). I was able to control the dissipation of 250W with these heatsinks: 

add me back on hackaday so that we can talk more, if you wish so.  

Hello Clovis, i'm fine, what about you?

Thanks for the heat sink recommendation,  i will probably increase the power capacity once i have a working controller. Which opamp/mosfet combination did you use?

Hi both of you,

I recently needed such electronics and ended writing this:

http://www.embeddedrelated.com/showarticle/775.php

Regarding the amplifer, an AD8552 is used for its very low

voltage offset, allowing for low load currents to be set. For

the transistor, a BTS117 is used.

The voltage sense does not exist, so I am very interested

about your controller.

Cheers