I designed a circuit to control the speed of a 24V coller. For this I used the operational amplifier
As I am going to control the output voltage through a PWM signal that comes from the STM32, it was necessary to create an RC filter to convert the PWM signal into analog.
0% duty cycle = 0V
50% duty cycle = 1.65V
100% duty cycle = 3.3V
I determined the gain of the amplifier as follows: Vo / Vi = (R30 / R27) +1
With that I have a gain of approximately 7.3. Theoretically for:
Vi = 0V ------ Vo = 0V
Vi = 1.65V ------ Vo = 12.045
Vo = 3.3V ------ Vo = 24.09
But this is not happening for input voltages near 0V. With the minimum input value I have at the 4V output and this affects the functioning of my system.
I know that there is a saturation in the amplifier that makes it never reach the maximum value of 24V. But I couldn't understand why for values close to 0V the output remains at 4V.