Please don't state the obvious that nothing is a perfect constant current source. And please do not give examples of how to create them from components.
I looked at this SE Q/A which stated the obvious – that you can not have a perfect current source.
So when I say constant current source, I am not referring to the mathematical concept used in circuits, but "natural" components that provide a close approximation to this. Key word is approximation.
A bit of research pulled up one interesting example which was a solar cell. Is this a valid example?
A google search pulls up a similar Quora question here. Which gave the example of a solar cell.
This is a more technical site and I was looking for a more engineering answer not a mathematical or laymen's answer.
Thanks.
Best Answer
Photovoltaic cells and betavoltaic cells are examples of devices that produce more-or-less constant current up to some maximum open-circuit voltage, just as a battery produces more-or-less constant voltage up to some maximum short-circuit current.