Question

In the given circuit both diodes are ideal having zero forward resistance and built-in potential of $0.7V$. Find the potential of point $E$ in volts.

Answer 1

Solution:

Step 1: Draw the required diagram:

Step 2: Explaining the diagram

1. Check the voltage at $E$ using nodal analysis on both the left and right sides. For nodal analysis the voltage at $B,F$, and $G$ will be $0V$, while the voltage at $A$ will be $12.7V$ and the voltage at $H$ will be $4V$.
2. Put the nodal from the right side then the voltage at $E$ will be $12$ volts (the diode between $A$ and $E$ will be forward-biased). Now that the voltage at $E$ is $12$ volts and the voltage at $H$ is $4$ volts, the diode between $E$ and $H$ is reverse biased, and any voltage difference is possible across reverse biased.
3. Thus, yes, it is a possibility.
   If we put the nodal from the left side then the voltage at $E$ will be $3.3volts$ (the diode between $E$ and H will be forward-biased). Now that the voltage at $E$ is $3.3volts$ and the voltage at $A$ is $12$ volts, the diode between $E$ and $A$ is forward biased, and a voltage difference of $0.7volts$ is permissible.
4. Thus, this case is dismissed. Therefore, the current will not flow through the $GH$.

Hence, the value of $V_E$ is $12V$.