I found this (description! of link in my post #7) see below:Good spot, I think you're right and I've edited the above post. Can we discover the relationship of resistor to current for Gen. 1 drivers?
My attempts at unravelling this from the 274uA current, (presumably from 12V) - and I really haven't understood this - suggested someting like 7V across Rset, which would be driving the lamp a bit over 400mA.
Post crossed with yours Lucien!
I thought I had worked out the source impedance of the 274uA and I had a potential divider of that and Rset which led to a voltage across Rset that I mention above.
Clearly something wrong with that!! Yes - it's a constant current source DUH! Prefer your version.
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