Fig 8: 8. Power MOSFET PWM Motor Driver
What you are trying to do is to convert a 0 ->100% PWM into a 0 ->
1.4A current source. Why?, why not convert your 0 -> 10V AC V into a
0 -> 1.4A current source. Or for a 1V ac input, are you are applying
your 300Hz based PWM directly to the solenoid, so for 1V (10%), a pulse
of 1.4A of .33mS length is applied every 3.3 mS?

If its just the 0 -> 10 V into a 0 ->1.4A, then build a
precision rectifier as per inventor(y)'s suggestion, then use an op-amp
with a power transistor using the solenoid as its collector load, and a
low value resistor (1 ohm) in the emitter circuit. So now you have a
monitoring point for the solenoids current. I've since been able to source suitable gate valves due to your help. However, I still have one problem. All the

At 1.4A out, there will be
1.4V dropped across this resistor. So connect your feed back resistor
from this point to the - input of the amp with another resistor to earth
also from the - input. These resistors set your range in terms of
Vin/Iout. Feed the actual voltage into the + input of the op-amp.

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