capacitor in opamp feedback

[electros6]

Hi guys,
         I many instruments where the reference value is compared with the actual value using op-amp and it is used to drive transistor of mosfet.  I such opamps a capacitor is used in the feedback loop to reduce the gain at higher frequencies. how to design such capacitor in the feedback loop.
                     

[T3sl4co1l]

The pole must be positioned either above or below the dominant pole of the driven system (transistor and whatnot).  Usually by a factor of 3 or so.

Or better yet, a pole-zero pair (using an R+C instead of C alone) can be positioned so that the zero cancels the system pole, and the remaining dominant pole sets the desired/required roll-off frequency.

I don't know what your transistor is driving, but a typical example would be a constant current sink, where the series resistor and gate capacitance form a dominant pole.

Tim