I've a question for you.
In the circuit shown below I've to find the values of Rin and Ro in order to have the maximum (20mA) and the minimum (4ma) output current on the load, with Vin swinging from 0V to 3V3. The OP-AMP has to be considered as an ideal OP AMP, and the BJT too. Can someone help me finding the solution? My problem is that I can't figure out how to consider the feedback ring. I've tried to put Vin to 0V. So I get 0V on V-, 0V on V+. Is it correct? The current Io on Ro is Vcc/Ro. The current on the "feedback ring" is Ifb= Io-IR2. And this is where I'm stuck. I've to put this current Ifb equal to what to solve the equation and get Ro?
In circuit like this one is it wrong to use the virtual ground aproximation? Is it beacause I have no negative feedback?
Thanks!!
In the circuit shown below I've to find the values of Rin and Ro in order to have the maximum (20mA) and the minimum (4ma) output current on the load, with Vin swinging from 0V to 3V3. The OP-AMP has to be considered as an ideal OP AMP, and the BJT too. Can someone help me finding the solution? My problem is that I can't figure out how to consider the feedback ring. I've tried to put Vin to 0V. So I get 0V on V-, 0V on V+. Is it correct? The current Io on Ro is Vcc/Ro. The current on the "feedback ring" is Ifb= Io-IR2. And this is where I'm stuck. I've to put this current Ifb equal to what to solve the equation and get Ro?
In circuit like this one is it wrong to use the virtual ground aproximation? Is it beacause I have no negative feedback?
Thanks!!