Current Sources

Sorry, now I'm back to square one again. :( Are we to take it, then, that Ralph's definition is incorrect in some way?

No. I was just offering another way of looking at it. ...Jim Thompson

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This is a bootstrap current source:

The idea is to keep a constant voltage across the left-most 1K resistor, so it dumps a constant 5 mA current into the 39 pF cap. That makes a linear voltage ramp.

Maybe a Howland current source circuit schematic (a variation on your scheme) would aid the OP in his understanding. ...Jim Thompson

Jim Thompson wrote on 9/24/2017 10:01 PM:

Yes, these circuits are exactly what a person who doesn't understand a current source would need to help them. NOT! lol

It's not incorrect if you understand it. A current source is just that, a source the supplies enough potential to drive a given current though a load regardless of resistance. You can think of this as a variable voltage source and a smaller resistor or you can think of it as a very large fixed voltage source and a very large resistor. Both do the same thing.

How about we turn this around and ask you how you see a current source? For that matter, why don't you explain to us what a voltage source is?

Right, I do that with a 5V reference (REF02 or similar) I'm guessing that it (REF02) would be slow compared to the LM4040... also has headroom issues.

George H.

What sort of application did you design this for?

Picosecond-resolution delay generators and time stampers. Both need fast linear ramps.