Zener Diode — Voltage regulation
Semiconductor
11
JEE Qs
8%
Hard
60
min
Always check the operating conditions of the Zener diode (is it in breakdown? is I_Z within limits?) before applying Zener regulation principles to solve problems.
🧮 Key Formulas
✅ Key Points for JEE
- 1A Zener diode is specifically designed to operate in the reverse breakdown region, maintaining a nearly constant voltage (Zener voltage, V_Z) across itself despite significant changes in current flowing through it.
- 2The series resistor (R_S) is essential in a Zener regulator circuit to limit the total current, drop the excess input voltage, and protect the Zener diode from overcurrent.
- 3For effective voltage regulation, the Zener diode must remain in its reverse breakdown region, meaning the input voltage (V_in) must be sufficiently high (V_in > V_Z) and the Zener current (I_Z) must be between its minimum knee current (I_Z_min) and maximum permissible current (I_Z_max).
- 4Zener regulators provide both line regulation (stabilizing output despite input voltage variations) and load regulation (stabilizing output despite load current variations), by shunting excess current through the Zener diode.
⚠️ Common Mistakes
- ✕Assuming the Zener diode is always in breakdown without verifying the conditions (V_in > V_Z and sufficient current to cross I_Z_min).
- ✕Incorrectly applying Kirchhoff's Laws (KVL/KCL) or Ohm's law to different parts of the Zener regulator circuit, especially regarding current division between Zener and load.
- ✕Ignoring the Zener's maximum power dissipation limit (P_Z_max) or minimum current (I_Z_min), leading to circuit failure or non-regulation.
📝 Practice Questions
See allQ27.Consider the following statements: A. The junction area of solar cell is made very narrow compared to a photo diode. B. Solar cells are not connected with any external bias. C. LED is made of lightly doped p-n junction. D. Increase of forward current results in continuous increase of LED light intensity. E. LEDs have to be connected in forward bias for emission of light. Choose the correct answer from the options given below: (1) B, E Only (2) B, D, E Only (3) A, C Only (4) A, C, E Only
Q43.Which of the following circuits has the same outpur as that of the given circuit? (1) (2) (3) (4)
Q33.Which of the following circuits represents a forward biased diode? Choose the correct answer from the options given below : (1) (A) and (D) only (2) (B), (D) and (E) only (3) (C) and (E) only (4) (B), (C) and (E) only
Q26. A B Y 0 0 1 0 1 1 1 0 0 1 1 1 To obtain the given truth table, following logic gate should be placed at G: 2025 (22 Jan Shift 2) JEE Main Previous Year Paper (1) OR Gate (2) AND Gate (3) NOR Gate (4) NAND Gate
Q28.The output of the circuit is low (zero) for : (A) X = 0, Y = 0 (B) X = 0, Y = 1 (C) X = 1, Y = 0 (D) X = 1, Y = 1 Choose the correct answer from the options given below : (1) (B), (C) and (D) only (2) (A), (B) and (C) only (3) (A), (C) and (D) only (4) (A), (B) and (D) only
Q45. In the circuit shown here, assuming threshold voltage of diode is negligibly small, then voltage VAB is correctly represented by : (1) VAB would be zero at all times (2) (3) (4)
NCERT Chapters
- Class 12 Physics Ch 14: Semiconductor Electronics: Materials, Devices and Simple Circuits