Both the diodes used in the circuit shown are assumed to be ideal and have negligible resistance when these are forward biased. Built in potential in each diode is $0.7$ V. For the input voltages shown in the figure, the voltage (in volts) at point A is ______.
Numerical value type. Enter your answer.
Answer: 12
The left diode conducts from the $12.7$ V input towards A, and the right diode would conduct from the $4$ V terminal towards A.
Suppose the left diode conducts. Then $V_A = 12.7 - 0.7 = 12$ V.
The right diode would then have $4$ V on its anode and $12$ V on its cathode, so it is reverse biased and carries no current. This is consistent.
(If only the right diode conducted, $V_A$ would be $3.3$ V and the left diode would be strongly forward biased, a contradiction.)
So $V_A = 12$ V.
Solution by Sreeraj P, M.Sc Physics