Voltage controlled current source circuit needed for high currents

[doncarlosalbatros]

crutschow and Klaus here is the reason I didnt use a non inverting opamp:

Simulations were not how I wanted.

If I use LMC6482 as in following way:


Here are plots for input to the non inverting input(blue), output of the op amp and the power dissipated:

As you see above output voltage is not pulled to zero also note that the pulses get distorted. And so much power is dissipated.

And if I use the following one:



Now the power dissipation is less but there is like 8mV offset again in the output when PWM is OFF. In INAMP it goes to zero.
I also tried with LM358 same issue.

Maybe better to draw a sketch of the topology what you mean if my circuit is wrong. Thanks.

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What Klauss is trying to say here:

is that your IRL3803 is already a logic level N channel mosfet (a very good one for this application by the way..), which means, you can drive it directly from the MCU_PWM pin with a properly selected resistor at the gate.

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That is necessary only if you implement the active low pass filter suggested by Klauss. If you stick with the Instrumentation OP amp, you are good...

I didnt get the last part. If I use the INAMP above the MOSFET as in my circuit, I cannot use an active filter? Better to draw than words I guess,

 

[CataM]

I didnt get the last part. If I use the INAMP above the MOSFET as in my circuit, I cannot use an active filter? Better to draw than words I guess,

Solution 1): you can use an active filter with high order (e.g. 3rd order suggested by crutshow) but with no gain. You can use a simple passive RC LPF.
Solution 2): doing it like Klauss suggested, current sensing must be on the soruce path.

 

[doncarlosalbatros]

How can I design an active 2nd order butterworth with gain for about 20Hz LPF?
Is there a practical tool for that when you plug in 20Hz cut off and gain it outputs the component values on a topology?

If I can have that I wouldn't need the -5V voltage converter and an INAMP.

 

[CataM]

How can I design an active 2nd order butterworth with gain for about 20Hz LPF?
Is there a practical tool for that when you plug in 20Hz cut off and gain it outputs the component values on a topology?

https://www.analog.com/designtools/en/filterwizard/

 

[crutschow]

This should help.

But I would go with a Bessel rather than a Butterworth response to minimize overshoot.