Constant Current cource for LED

[pratikb]

Hello,
I am creating a constant current source for LED to use it as a constant light source for Biosciences experiments.
I have designed a circuit in which there is a Voltage Reference IC 5025I(Texas Instruments) which will provide me with a constant voltage of 2.5 V.
This 2.5 V will be converted into a constant 25 mA current with the help of a high precision V-I converter XTR111(Texas Instruments) which will be further connected to an LED for constant light source.
I have attached my schematic.
The problem I am facing is that there is no output current or voltage to load.
The XTR111 IC is heating a lot!
The ref5025 IC gives proper output when XTR111 is not connected, but just when XTR111 is connected, values of output current,voltage become zero
The Power supplies are as follows:
24V supply for XTR111
5V supply for voltage regulator of XTR111
3.3V supply for REF5025I

 

[KlausST]

Hi,

the XTR111 is made for analog signal transmission with 4..20mA current loops.

You use it as LED constant current source.
In my eyes this is a expensive solution, but it shoud work.

==> REGF is an OUTPUT. don´t supply it with external 5V. Check this.

[added: ==> OD is an input. to enable output you have to connect it to GND.]

VSP input voltage range is 7V...44V. By supplying it with 24V and a current of 25mA there is 0.6W of dissipated power. Maybe you can lower supply voltage.

Klaus

 

[Externet]

That is complex way to turn on a led. If there is no feedback from lumens reaching the target, illumination will not be very constant as desired due to temperature/distance...
Or, keep it simple----> https://www.onsemi.com/PowerSolutions/parametrics.do?id=197