Hi!
I have a Wheatstone bridge (120 ohm) powered by 3.4 V.
I'm trying to obtain a voltage of circa 0.4 V in node A, as you can see in the attached circuit.
So I decided to use an adjustable 3-terminal positive voltage regulator (LM317LZ) and two resistors in order to have an output of 0.4V. This voltage is applied to the non-inverting terminal of op-amp and the inverting terminal is connected to node A. To accomplish my goal a current has to flow from VDD towards the BJT, so the BJT must be on!
I'm trying in every way! But I don't understand why I am mistaken...
Maybe I have to pay attention to the input common-mode voltage range of the op-amp. That in the circuit is a rail-to-rail op-amp, but it is only an example. I don't know if it could be a possible solution.
Maybe I need a resistor between the output of op-amp and the base terminal of the BJT.
Have you any ideas? I don't know what is wrong.
Thanks!
I have a Wheatstone bridge (120 ohm) powered by 3.4 V.
I'm trying to obtain a voltage of circa 0.4 V in node A, as you can see in the attached circuit.
So I decided to use an adjustable 3-terminal positive voltage regulator (LM317LZ) and two resistors in order to have an output of 0.4V. This voltage is applied to the non-inverting terminal of op-amp and the inverting terminal is connected to node A. To accomplish my goal a current has to flow from VDD towards the BJT, so the BJT must be on!
I'm trying in every way! But I don't understand why I am mistaken...
Maybe I have to pay attention to the input common-mode voltage range of the op-amp. That in the circuit is a rail-to-rail op-amp, but it is only an example. I don't know if it could be a possible solution.
Maybe I need a resistor between the output of op-amp and the base terminal of the BJT.
Have you any ideas? I don't know what is wrong.
Thanks!