Which one is better? (with or without output transistor)

[jawadlateef]

Hi all,

I am interested in current output that will be in different stages from 0-1mA, 0-100uA and so on. which is being selected by Q6 through Q9.
The pot at the non inverting input varies the voltage and so that it effects the output of the opamp.
The voltages at the nodes a,b,c and out is same with BJT at output or without. Please suggest me which method is better and why?

I shall be very grateful to you

Regards

 

[Grossel]

None is better. For the type of schematics you post, PNG format would be much better than JPG considering file size and losses of quality.

Is this circuit ment to be a step regulated current source?

If that's the case, I would done it otherwise. I would have used either a jfet or a darlington bjt in this manner: