3-4) Zener Diode

Question 1

What is unique about zener diodes?

Answer 1

They are designed to operate in the reverse biased breakdown region.

Question 2

What is the typical voltage drop of a forward biased zener diode?

Answer 2

0.7V

Question 3

Under what conditions does a zener diode begin to conduct current?

Answer 3

When reverse-biased, zener diodes only begin to conduct current when the zener voltage is reached. The voltage drop across the zener diode will also be constant at the fixed zener voltage. As long as the power dissipated by the current flowing through the zener when reverse biased does not exceed the diode’s thermal limits, the diode will not be damaged.

Question 4

What is the typical range of available zener voltages?

Answer 4

From a few volts to hundreds of volts.

Question 5

In this parallel circuit with a zener diode, determine the following:

• Voltage Drop: R1, R2, R3, D1
• Current: R1, R2, R3

Answer 5

1. R_T = R₂ + R₃ = 15K
2. I_R2-3 = V_D1 / R_T = 0.2mA
3. V_R3 = 5,000 x 0.2mA = 1V
4. V_R2 = 10,000 x 0.2mA = 2V
5. V_R1 = Applied Voltage - VD1 = 12V - 3V = 9V
6. IR1 = 9V / 10K =0.9mA