Download Slide 1 - IIE

EELE 2321 – Electronics
Spring, 2013
Zener Diode
Eng. Wazen M. Shbair
Content
 Zener diode principles
 Zener diode application
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
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.
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Zener diode V-I characteristics
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
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
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Breakdown Characteristics
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
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
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Zener Equivalent Circuits
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Zener Equivalent Circuits
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Example
 Calculate Zener impedance
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
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
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Example
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
Zener Power Dissipation
 Zener diodes are specified to operate at a
maximum power called the maximum dc
power dissipation, PD(max).
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
ZENERDIODE APPLICATIONS
The zener diode
can be used as
a type of voltage
regulator for
providing stable
reference
voltages
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
From No Load to Full Load
 Example 3.5
 Zener Regulation with a Variable Load
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.
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)
Electronic Devices, 9th edition
Thomas L. Floyd
© 2012 Pearson Education. Upper Saddle River, NJ, 07458.
All rights reserved.