Here's a circuit using a non-inverting Deboo (Howland) integrator if you want a linear ramp but, as you can see, it's a bit more complicated, requiring an op amp..

 

Thank you. That looks a lot closer to what I was trying to accomplish. I'll run that one was well.

 

Thank you. That looks a lot closer to what I was trying to accomplish. I'll run that one was well.

If you want a full 12V out, you will need a rail-rail type op amp, such as the one in the simulation.
A single-supply but not rail-rail op amp, such as the LM324, will have a maximum output of about 10.5V.

 

Ah, i was wondering how you got the full voltage.

 

Ok so I was able to Sim the circuit but only after giving an independant battery source like in the schematic. Is it safe to assume that the battery source would be rail power waiting while the "ramp" voltage would a input trigger?

 

I was able to Sim the circuit but only after giving an independant battery source like in the schematic.

Why would you try it without?

Is it safe to assume that the battery source would be rail power waiting while the "ramp" voltage would a input trigger?

Yes, the battery is a constant supply voltage for the op amp.
The input is either 12V or 0V.
The op amp output is the ramp, which ramps up for a 12V input, and ramps down for a 0V input.

 

I hope I can make this clear. If the power is on, and the pwm is called for, all is well... The op amp has power waiting and the new circuit in place of the poentiometer is called for, it works like the Sim.

However, if power is turned on at the same time that the circuit is called for, then the result is erratic. I will have to find a way to provide power to the op amp and stop the "call" of the "pot" until the op amp is ready.

 

You shouldn't need a delay for power up since the op amp will be ready as soon as it has power.

If you need to shut off the 12V power to the op amp upon shutdown, they you could use a series diode and large capacitor to ground at the op amp power pin to supply power for the few seconds the down ramp takes.

Below is the circuit powered from the 12V input pulse with a diode and capacitor to provide op amp power during the ramp-down.

 

Ok I see how that works. That should be good to cover that situation. Thank you!