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Current sink circuit

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jimmykk

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Hi

I was looking into this circuit for constant current sink and was wondering about the working
and output voltage of this circuit.
tltl.PNG
I am trying to implement this circuit and in my case the input voltage will be bit higher(<10v).
How would this affect the circuit. Sink current(Io) should be connected to negative of battery?
 

Hi,

A couple of hours we had about the same discussion: https://www.edaboard.com/showthread.php?382814-Lm317-input-and-output-pin-voltage-specification

In short: The device regulates for a constant voltage across two of it's pins. If you now connect a resistor across these two pins: Then (according Ohm's law) you get a constant current.

output voltage of this circuit.
Click to expand...
As this is a constant current circuit, it does not care about input voltage. It just regulates the current. (As long as it is able to)

Klaus
 

KlausST said:
In short: The device regulates for a constant voltage across two of it's pins. If you now connect a resistor across these two pins: Then (according Ohm's law) you get a constant current.
Click to expand...

You mean if i connect resistor between pin: Vi(batt) and Io as per circuit above?
 

Hi,

No,

See the circuit above:
* TL43xx is the voltage regulator. Please read it´s datasheet about it´s operation.
* Rs is the resistor that determines the constant current, because the TL43xx regulates a constant voltage across Rs. I = V / R

Klaus
 

I get that Rs determines the Io. But one thing that is unclear to me is the collector of that transistor.
Should it be connected to a load ....
 

Hi,

Should it be connected to a load ....
Click to expand...
I wonder about this question. How should I understand it?
What else do you want to do with a constant current circuit?
And if it was not your inital plan to connect it to a load .. why did you choose this circuit?

It´s like buying a TV set and asking: What to do with it - should I watch TV?

Klaus
 

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