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

EELE 2321 – Electronics Spring, 2013 Zener Diode Eng. Wazen M. Shbair. Content. Zener diode principles Zener diode application. Zener diodes.

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

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  1. EELE 2321 – Electronics Spring, 2013 Zener DiodeEng. 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)

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