These are breakdown voltages.
Look at page 2:
http://www.farnell.com/datasheets/296640.pdf (don't worry, it's the same part, just the old metal envelope)
Saturation voltage 0.6V at 15mA, and it decreases when current decreases (we're looking at 1mA or so here). Also Darlington is configured so that the saturation voltages are stacked (both transistors need to be turned on), so that adds up to about 1.13 or so. It does depend a bit on what production batch and manufacturer you get.
Once again, it's not so sensitive. Just use 1.14 or 1.15 or whatever. Even if you use 0.1% resistors, the FET and the transistors have temperature coefficients, so the current is never going to be 100.00% where you plan it to be. Close enough is good enough.
I don't know what the context is for my statement. But you can just pick a current you like, and use the formula. It'll be ok. 0.3mA here or there is not going to matter much.
I'm very happy to hear that!
Have you thought about the external functioning of the CCS? As in, imagine it's a module, a box dropped in the circuit; what does it do, what is it's function in the circuit?
Click to expand...