LOL, your hurting my head...I will do a diagram and then make some options etc and we can have several diagrams for folks to follow..One could design a much better DC voltage source using a L293D or L9110H bridge driver, but using just one transistor this is probably the easiest.
If one needs voltages below 0.8V or more linearity above 9.0V one could modify a few more things (exchange the 2N2222A npn-transistor for an n-channel MOSFET like the 2N7000, can be plugged in the exact same place and wont need the resistor to the PCA9685; as well as using a Shottky diode like a 1N5817 instead of a regular rectifier diode like 1N4001).