some circuits use transistor as a high load to make the gain high in op amp circuits so how it works and i am looking for circuit explain this so if any body can help me
thanks

 

Please don't post the same question twice; it makes for confusion and board clutter.

Transistors, Darlingtons or MOSFETs can be used to either sink or source much more current than an opamp could by itself.

It depends upon what opamp you are using, and how much current you need to source or sink as to what might be the best approach.

You will need to describe what you wish to do more completely.

What voltage(s) do you have available?
How much current do you need to either source to, or sink from, your load?