Q56 / 75 · JEE Main 2026 (28 January Shift 2) · Physics

Two p-n junction diodes $D_{1}$ and $D_{2}$ are connected as shown in figure. $A$ and $B$ are input signals and $C$ is the output. The given circuit will function as a $\_\_\_\_$.
Figure

  • A
    NOR Gate
  • B
    NAND Gate
  • C
    OR Gate
  • Correct answer
    D
    AND Gate

Solution

If $A = 0$ and $B = 0$: Both diodes are forward biased. The potential at $C$ is pulled down to approximately $0V$ (logic 0).
If $A = 0$ and $B = 1$: Diode $D_1$ is forward biased, pulling the potential at $C$ down to $0V$ (logic 0). Diode $D_2$ is reverse biased.
If $A = 1$ and $B = 0$: Diode $D_2$ is forward biased, pulling the potential at $C$ down to $0V$ (logic 0). Diode $D_1$ is reverse biased.
If $A = 1$ and $B = 1$: Both diodes are reverse biased. No current flows through the resistor $R$, so the potential at $C$ remains at $V_{dc} = 5V$ (logic 1).
The truth table is:
 A  B  C 
000
010
100
111

This truth table corresponds to the AND gate logic operation $C = A \cdot B$.
Therefore, the circuit functions as an AND gate.

Hence, the correct answer is option: 'D'.

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