10mA constant current source independent of load (10 ohm to 5k ohm)

Hi Umesh!

10mA through a 5kohms resistor would cause a voltage of 50V. 10ohms to 5kohms is a very wide range. And something around 50V is beyond the LT1002's operating range. What is your actual supply for the OPAMP? Just for testing the concept of your current source you can use an ideal OPAMP instead of a specific part.

Dennis

Look at this basic working principle - the load (R2) is not GND referenced now.

For a load of 10ohms:

And for a load of 5kohms:

As you can see, the current through R2 is ~10mA for both cases. The reason for not being exactly 10mA is the base current into the transistor that comes from the OPAMP. A MOSFET can be used instead - it has no gate current, so all the current must run through R2 as well. But this is just an example of another topology.

Note that the BJT / MOSFET must handle about 0.6W for the case of a 10ohms load. And of course the device must be able to withstand the voltage. But for 10mA and 5kohms you will need at least about 55V coming from the supply.

Dennis

For floating load we can use this simple circuit . It gives 10mA constant over 10-5k load

Umesh Patil10 said:

But I have not understood what you mean to say disabling self likes.

I mean to revise this:

Umesh Patil10 said:

For floating load we can use this simple circuit . It gives 10mA constant over 10-5k load

You might be able to use it for a load of 10ohms, but not for 5kohms. The OPAMP's output would need to be -50V in this case.

Dennis

Umesh Patil10 said:

I think for grounded load the supply voltage must be at least 50 V.

No matter what you do, 10mA through 5kohms is always 50V voltage drop.

Usually, every precision OpAmp example is a calculation based and Ohm's law is always in rule: V=I*R.