I'm not sure what I'm looking at with the circuit you posted. I don't see any PWM. I see the blue trace going from 0-12, which I assume is supposed to be the PWM (but isn't) and the green trace going from 6 to 9 which I assume is the analog output.

Can you please post your simulation so I can play with it?

Doing a simple low pass filter will give me 0-12v which will only work if i limit my pwm signal to from 50% - 75% which will severely limit the precision i need(I assume)

You mention you are concerned about precision. I anticipate this circuit will be slow to respond (inaccurate any time not in steady state). That is why I recommended the LTC2645. It will respond instantly.

 

I commented on the precision of only using a LPF, which would of given me 0-12v dc, with PID loop it would have found its speed eventually after going from 0-12. I wasn't aware I could level shift so easily.

 

So after 17 posts we find out what the real requirements are.

Seems about normal.

 

Can you attach your simulation? No reason not to, not like it's sensitive IP or anything, we've already all seen it. I could recreate it in Ltspice but I'm not going to.

 

Sim attached

 

Your simulation was not providing a PWM signal. It was providing an analog ramp from 0-12V.
I've adjusted the simulation to provide a real PWM signal (50% duty cycle @ 490Hz).
You can see below, the PWM is set to turn on at the 100mS mark. This is to illustrate the response time of the circuit.
The analog output does not stabilize until about the 400mS mark.
Is 300mS of response lag acceptable to you?

 

Same circuit, 90% duty cycle

 

View attachment 140586
Same circuit, 90% duty cycle

It willbe fine for my application

 

So when I connect the valve to the output it pull the signal down from 6v to 3v. Im not sure if this can be fixed using lower value resistors or if I will need to add an opamp.

Please advise

 

You could try lowering your resistor values or add an opamp to the output

 

So when I connect the valve to the output it pull the signal down from 6v to 3v. Im not sure if this can be fixed using lower value resistors or if I will need to add an opamp.

Please advise

I've re-run the sim to give a 6V output (0-5% PWM), then started adding resistance to the output to see what it takes to drag it down to 3V.
Looks like the valve input has about 30k of impedance.


The reason it draws down so far is because the very high resistor values in your circuit.

Then I halved the values of all your resistors and gained about 1V.

Halved them again, and there was very little gain.

Here is the result with all resistor values 25% of original value.




Then I went back to your original circuit values and added a non-inverting amplifier with unity gain and re-ran with 30k impedance.
perfect result.





I think you are going to have to use an opamp despite how badly you seem to not want to.

 

Alright, I will give it a go as soon as I can and report back. Thanks for your help.