The proposed LED intensity controller circuit may be learned as shown in the diagram.
Two diagrams can be seen, the left hand side may be used for controlling common anode type displays while the right hand side for common cathode types.
The design is basically a common collector BJT circuit where the base potential of the relevant transistors get proportionately delivered across their emitter base terminals.
Thus by varying the potential at their bases the emitter potential is also proportionately varied with a range right from 0V to the maximum supply voltage level (-0.7V).
Each of the following LED intensity controller modules could be used for the proposed 7 segment LED display control application. The preset may be replaced with a pot and its dial appropriately calibrated for getting the intended varying illumination through a range of 0 to 9.