Electronic – What’s the point of a current source

current-source

schematic

simulate this circuit – Schematic created using CircuitLab

OK. So I've been told that the current flowing into the current source (that is, into the arrow's behind) is the same as the current coming out of the current source (that is, out of the arrow's head).

If this is the case, then why is it a current "source"? It's not providing any extra current!

I know this is a fairly elementary question, but I haven't found a good answer elsewhere.

Thanks.

Best Answer

The current in any 2 terminal device is always the same, there's no way for a 2 terminal device to provide "extra" current. You can't have 0A in and 4A out.

What it does do is force the current to be the given value regardless of the impedance across it. (So therefore you can't put in an open circuit an ideal current source, the voltage would go to infinity.)

So a resistor by itself has no current through it. Hook it across an ideal current source and you get (for your example current source) 1A through it regardless of the value of the resistor.