Why is the following circuit an adjustable current limiter? It looks like a adjustable current source to me.
EDIT: I know the difference between current limiters and current sources. Lets analyze the circuit the clear up some misunderstandings.
From the datasheet: "In operation, the LM150 develops a nominal 1.25V reference voltage, VREF, between the output and adjustment terminal.".
I think that R2 in combination with the diodes and jfet is used to superimpose a voltage on top of the adjust terminal so that the voltage over R1 decreases, which in turn limits the current that can flow through R1. This sets an upper limit for the current, but what happens if output current is less than current that we can draw? Since the difference between output and adjustment terminal is set to 1.25V and a voltage forced on top of the adjust terminal (and thus over R1), what is left to change to downregulate the current? The only thing I can come up with is that the excess current needs to be sinked, but where?
Best Answer
A current limiter is a current source with a limited voltage compliance. All practical current sources have this limitation, so they are current limiters.
Consider the humble current-limited lab supply. Set its current limit to 20 mA, and voltage at 5 V, and now it's a constant-current source for testing LEDs.
(answers with pictures get upvotes!)