Hi! Anyone have schematic for lm317 as current limiter? The two photos from datasheet, one is current regulator and one is current limiter but it loooks the same except for the potentiometer??
What's the difference in these two circuits? Why would one act as limiter by just changing resistor to potentiometer?
The potentiometer just makes the current adjustable.
groundfungus:
The potentiometer just makes the current adjustable.
Yes but it says current limiter. What it really does is adjust constant current output, same as the other circuit with just resistor.
Of course.
There is no difference between a "current limiter" and a "current regulator". There can not be. Regulating is limiting, simple as that.
You should really forget about that circuit. It is next to useless. It has a voltage penalty of about 2.7V (at 20mA, 3.7V at 1.5A) with the LM317; that is, the minimum voltage lost in the drop-out of the regulator plus the 1.25V wasted in the resistor.
This would be the preferred circuit, with a drop-out voltage of something like 1V: (Ignore the minimum current resistor and "back EMF" diode unless they are required for some reason.)
Paul__B:
Of course.There is no difference between a "current limiter" and a "current regulator". There can not be. Regulating is limiting, simple as that.
You should really forget about that circuit. It is next to useless. It has a voltage penalty of about 2.7V (at 20mA, 3.7V at 1.5A) with the LM317; that is, the minimum voltage lost in the drop-out of the regulator plus the 1.25V wasted in the resistor.
This would be the preferred circuit, with a drop-out voltage of something like 1V: (Ignore the minimum current resistor and "back EMF" diode unless they are required for some reason.)
Thanks for the schematic, im gonna try that.
I thought current limiter and current regulator(constant current??) are different.
On a current limiter I can set the max current that i want and the current will not go above that, on a constant current it will output(or try) the set current no matter what the load is??
The diagram that I posted labeled current limiter is forcing the set current to the load not just limiting it, that's not what i want.
Tamulmol:
On a current limiter I can set the max current that I want and the current will not go above that, on a constant current it will output (or try) the set current no matter what the load is??
Absurdly wrong.
If the load resistance is too high, the voltage source always will be unable to force more than a certain current through it, according to Ohms Law (which you surely must know). It is the "or try" that catches you. 
The two descriptions merely describe the two alternative states of the circuit. A "current limiter" is intended to normally work in maximum voltage state, whilst a constant current circuit is intended to work in - a constant current state. But the circuits are identical.
The tricky part is when you wish to current limit a voltage-regulated power supply, as you have to design it such that the current limiting circuit does not degrade the regulation by placing the "sense" resistance in series with the output. Conversely, if you sense the voltage after the current-limiting stage, the current drawn by the voltage feedback circuit becomes part of the current that is being limited, which rarely matters for large current values, but is significant where you wish to limit the current to mere milliamps.
Hmmm so it's not as simple as a current limiter limits current and constant current gives constant current? Thanks for the replies! I need to read a lot before i build my own power supply 
Groundfungas answered your question in Reply#1
Hmmm so it's not as simple as a current limiter limits current and constant current gives constant current?
The circuit you are asking about is the circuit used in bench LAB Power Supplies that have adjustable voltage and adjustable current . (separate knob for each). This differs from a standard regulator that only regulates voltage.
Adjustable CURRENT Variable Voltage Bench Lab PS
I am sorry but at the moment I don't have a link to a DIY version. I'll see what I can find but you can try
Googling it. Take a look at these.
This might be what you are looking for.
I should clarify that Ohm's Law states that your load resistance = R, the current through R =Vin/R. So increasing the current of the input increases the voltage drop across the resistor because Vload = Iload * Rload. If for example, you connect a 220 ohm resistor to a variable voltage , adjustable current bench lab supply, Ohm's Law states that at 5V, the current will be 5V/220 ohms =0.0227 A (22.7 mA. So the maximum current that you will ever draw from that load is 22.7 mA it you set the voltage to 5V. The current adjust knob will allow you to DECREASE the current but NOT increase it if the voltage is 5V. In order to INCREASE the current , you would need to INCREASE the voltage, for the same reason. What does this mean ? It means that if your objective is LIMIT the current through a fixed load , a simple adjustable regulator like the LM317 will do just fine. If you wanted 45.45 mA through the same 220 ohm resistor, you would simply adjust the LM317 to (2*5V)=10V. Having the ability to adjust both current and voltage is only useful if you want the current to be LESS than Ohm's Law says it would be at the target voltage (ie: 5V). If you test two Lm317 regulator circuits, the one you posted , and the conventional standard circuit shown on the datasheet with the same load resistance, if the two circuits were covered up so you couldn't see which is which and you measured the voltage across the load and the current through the load for both of them, you would see the same thing. You can say you are adjusting the current on the current limiter circuit, but it will will still show 10V on the output if you adjust the current for 45.45 mA. You can say you are adjusting the voltage on the standard voltage regulator but it will still draw 45.45 mA at 10V. So what is the difference ?
With the current limiting circuit you can set the voltage to 10V and limit the current to anything LESS than 45.45mA, whereas with the simple voltage regulator you can only adjust the voltage.
