LED Driver alternative

Lucien Nunes said:

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?

Click to expand...

I found this (description! of link in my post #7) see below:
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.

Oops, post crossed with yours.

It seems the Gen1 interface sets the fraction of the rated output current, not the absolute current, in the relationship: Iout = Inom ((Vset-1)/9). Vset can be derived from an active voltage source in a remote control, optionally referenced to the driver's +12V aux supply, or can be created passively by a resistor driven by a constant 274μA bias current that flows out of the control terminal. Thus for a 16kΩ resistor:
Vset = 274μ * 16k = 4.4V
Iout = 700 * ((Vset-1)/9) = 263mA

That's an even lower fraction of the panel's rating and is starting to sound unlikely.

To set a Gen1 driver of 700mA rating to 605mA with a resistor, one would need:
Vset = 605/700 * 9 +1 = 8.8V
Rset = Vset/274μ = 32kΩ or 33kΩ as the nearest preferred value.

Perhaps we are not seeing the colours on the resistor correctly, but I can't resolve them to anything like 33kΩ