Clarence Zener first described the breakdown of insulators in 1934, which was later used by Bell Labs to develop the Zener diode. A Zener diode allows current to flow in both the forward and reverse directions if the reverse voltage exceeds the Zener voltage. It acts as a voltage regulator by maintaining a nearly constant voltage across its terminals over a range of reverse currents.

1. ZENER DIODE

3. Clarence Melvin Zener was the American physicist who first (1934) described the property concerning the
breakdown of electrical insulators. These findings were later exploited by Bell Labs in the development of
the Zener diode, which was duly named after him.

4. ZENER DIODE
• A Zener diode is special heavily doped P N diode.
• A Zener diode is a special silicon pn junction device that allows current to flow not
only in the forward direction like a typical silicon or germanium diode, but also in the
reverse direction if the voltage is greater than the breakdown voltage known
as Zener knee voltage or simply Zener voltage
• A Zener diode operating in breakdown acts as a voltage regulator because it
maintains a nearly constant voltage, which is equal to the Zener voltage, across its
terminals over a specified range of reverse-current values.

5. DIFFERENCE BETWEEN PN DIODE AND ZENER DIODE

7. V I CHARACTERISTICS OF ZENER DIODE

8. ZENER DIODE AS A VOLTAGE REGULATOR
1. I=Iz+IL Kirchoffs current law
1. I=(Vi−Vz)/Rs ohms law = 24-
12/200= 0.06A 60mA
3. Vz=Vo …. Zener diode is connected
in
parallel with the load
resistor RL
4. IL=Vo/RL=Vz/RL
Conditions
1. When input voltage Vi is constant but load resistance RL is
changing.
2.When input voltage Vi is changing but load resistance RL is
constant.

9. • Vin = 30V , Rs=400 ohms, Izmin = 1mA, Izmax
= 50mA, Vz=10V and
• Find ILmin Ilmax , Rlmin, Rlmax

10. VIN = CONSTANT AND RL INCREASES
• If RL IL
• I is constant as Vin is constant
• I=Iz+IL
• Iz e.g 10=8+2
• 10= 9 +1
• If RL IL
• I is constant as Vin is constant
• I=Iz+IL
• Iz e.g 10=6+4
• 10= 4+6
VIN = CONSTANT AND RL DECREASES
CONDITION 1

11. VIN = INCREASES AND RL CONSTANT
• If Vin then current I
• IL is constant as RL is constant
• I=Iz+IL
• Iz e,g, 10=8+2 12= 10+2
• If Vin then current I
• IL is constant as RL is constant
• I=Iz+IL
• Iz e.g 10 = 8 + 2
VIN = DECREASES AND RL CONSTANT
CONDITION 2

12. AVALANCHE BREAKDOWN
12

13. ZENER BREAKDOWN

14. •R=V/I R is directly proportional
to V
• R is inversely proportional
to
I
•Rmax= Vmax/Imin Rmin =
Vmin/Imax