You need at least 5.5 to 6V on the LM4040 cathode, if the supply V fell below 5V the LM4040 cannot amplify it back up to 5. I would use a 4.096V LM4040. You have a 5:1 divider so 12V will be reduced to 2.4V.
You need at least 5.5 to 6V on the LM4040 cathode, if the supply V fell below 5V the LM4040 cannot amplify it back up to 5. I would use a 4.096V LM4040. You have a 5:1 divider so 12V will be reduced to 2.4V.