You have two outputs connected together, a great way to screw up components.
I guess you're referring to the connection of the PWM pulse Grumpy_Mike? - if not, I would like to know where I've done wrong :-)
As I described I was playing around with the constant current driver circuit found at Pcbheaven here:
Constant current driver
And then, on this page the guide says that
the best position to inject the PWM pulses is the gate of the MOSFET. The gate resistor RG will act as a pull-up resistor for the PWM generator.
Found in the bottom of the page: PWM
I believe I did it right following the guide at PCB heaven, but as far as I can tell from your comment, it isn't right at all. I would like to know what to do then. :)
You're absolutely right, the 2.1 was a typo (fixed now). If it's less than 1.2V which I haven't really thought of, that explains a lot, thanks for clearing that out :) !