1. EELE 2321 – Electronics Spring, 2013 Zener Diode Eng. Wazen M. Shbair

2. Content
Zener diode principles
Zener diode application

3. Zener diodes
A major application for zener diodes is as a type of voltage regulator for providing stable reference voltages for use in power supplies, voltmeters, and other instruments.
A zener diode is a silicon pn junction device that is designed for operation in the reverse-breakdown region.

4. Zener diode V-I characteristics

5. Breakdown Characteristics
As the reverse voltage (VR) is increased
the reverse current (IR) remains extremely small up to the “knee” of the curve.
The reverse current is also called the zener current, IZ.
At this point, the breakdown effect begins;
the internal zener resistance, also called zener impedance (ZZ), begins to decrease as the reverse current increases rapidly

6. Breakdown Characteristics

7. Zener Regulation
The ability to keep the reverse voltage across its terminals essentially constant is the key feature of the zener diode.
A minimum value of reverse current, IZK, must be maintained in order to keep the diode in breakdown for voltage regulation.
When the reverse current is reduced below the knee of the curve, the voltage decreases drastically and regulation is lost.
a maximum current, IZM, above which the diode may be damaged due to excessive power dissipation

8. Zener Equivalent Circuits

9. Zener Equivalent Circuits

10. Example
Calculate Zener impedance

11. Temperature Coefficient
The temperature coefficient specifies the percent change in zener voltage for each degree Celsius change in temperature.
For example, a 12 V zener diode with a positive temperature coefficient of will exhibit a 1.2 mV increase in VZ when the junction temperature increases one degree Celsius

12. Example

13. Zener Power Dissipation
Zener diodes are specified to operate at a maximum power called the maximum dc power dissipation, PD(max).

14. ZENERDIODE APPLICATIONS
The zener diode can be used as a type of voltage regulator for providing stable reference voltages

15. From No Load to Full Load
Example 3.5
Zener Regulation with a Variable Load

16. From No Load to Full Load
When the output terminals of the zener regulator are open
the load current is zero and all of the current is through the zener;
When a load resistor is connected,
part of the total current is through the zener and part through
The total current through R remains essentially constant as long as the zener is regulating.
The zener diode continues to regulate the voltage until reaches its minimum value, At this point the load current is maximum, and a full-load condition exists.
Example 3.6, 3.7(very important)