ELECTRONICS 1 - ceng.tu.edu.iq

ELECTRONICS 1

Lecturer:

Yaroub Ghazi

1

Tikrit University

Electrical and Electronic Engineering Department

Second Year

LECTURE 6: ZENER DIODE

ZENER REGION

WHEN THE APPLIED REVERSE POTENTIAL BECOMES MORE AND MORE NEGATIVE,

A FEW FREE MINORITY CARRIERS HAVE DEVELOPED SUFFICIENT VELOCITY TO

LIBERATE ADDITIONAL CARRIERS THROUGH IONIZATION.

WHEN VZ DECREASES TO VERY LOW LEVEL, THIS MECHANISM, CALLED ZENER

BREAKDOWN, WILL CONTRIBUTE TO THE SHARP CHANGE IN THE CHARACTERISTIC.

IT OCCURS BECAUSE THERE IS A STRONG ELECTRIC FILED IN THE REGION OF THE

JUNCTION THAT CAN DESTROY THE BONDING FORCES WITHIN THE ATOM AND

“GENERATE” CARRIER. DIODE EMPLOYING THIS UNIQUE PORTION OF THE

CHARACTERISTIC OF A P-N JUNCTION ARE CALLED ZENER DIODES.

ZENER DIODE

• THE ZENER DIODE IS A DEVICE THAT IS DESIGNED TO MAKE FULL USE OF THIS

ZENER REGION. ZENER REGION OCCURS AT A REVERSE BIAS POTENTIAL OF VZ.

ZENER DIODE APPLICATIONS

1- AC VOLTAGE REGULATORS (LIMITERS OR CLIPPER)

TWO BACK-TO-BACK ZENER CAN BE USED AS AN AC REGULATOR OR A

SIMPLE SQUARE WAVE GENERATOR AS SHOWN

A. SINUSOIDAL AC REGULAROR

ZENER DIODE APPLICATIONS

B. SIMPLE SQUARE WAVE GENERATOR

ZENER DIODE APPLICATIONS

2- DC VOLTAGE REFERENCE

TWO OR MORE LEVELS CAN BE ESTABLISHED BY PLACING ZENER DIODE IN A

SERIES AS SHOWN IN FIGURE AS LONG AS VI (E) IS GREATER THAN THE SUM OF

VZ1 AND VZ2, BOTH DIODE WILL BE IN BREAKDOWN STATE (ON STATE) AND THE

THREE REFERENCE VOLTAGE WILL BE AVAILABLE.

ZENER DIODE APPLICATIONS

3- DC VOLTAGE REGULATORS

A. FIXED VI, VARIABLE RL

𝐼𝑆 =𝑉𝑖 − 𝑉𝑍𝑅𝑆

(𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡)

𝐼𝐿(MIN) = 𝐼𝑆 − 𝐼𝑍𝑀

𝑅𝐿(𝑚𝑎𝑥) =𝑉𝑍

𝐼𝐿(𝑚𝑖𝑛)

𝐼𝐿(𝑚𝑎𝑥) = 𝐼𝑆 − 𝐼𝑍𝐾

𝑅𝐿(𝑚𝑖𝑛) =𝑉𝑍

𝐼𝐿(𝑚𝑖𝑛)

Example:

(a) For the network of Figure, determine the range of RL and IL that will result in VRL

being maintained at 10 V.

(b) Determine the maximum wattage rating of the diode.

Solution:

(a)

𝑅𝐿(𝑚𝑖𝑛) =𝑅𝑆𝑉𝑍𝑉𝑖 − 𝑉𝑍

=(1 𝑘Ω)(10)

50 − 10=

10 𝑋 103

40= 250 Ω

𝑉𝑅𝑆 = 𝑉𝑖 − 𝑉𝑍 = 50 − 10 = 40 𝑉

𝐼𝑅𝑆 =𝑉𝑅𝑠𝑅𝑆

=40

1 𝑘Ω= 40 𝑚𝐴

𝐼𝐿(𝑚𝑖𝑛) = 𝐼𝑅𝑆 − 𝐼𝑍𝑀 = 40 − 32 = 8 𝑚

𝑅𝐿(𝑚𝑎𝑥) =𝑉𝑍

𝐼𝐿(𝑚𝑖𝑛)=

10

8 𝑚𝐴= 1.25 𝑘Ω

(b)

𝑃𝑚𝑎𝑥 = 𝑉𝑍𝐼𝑍𝑀 = 10 32 𝑚𝐴 = 320 𝑚𝑊

B. FIXED RL, VARIABLE VI

• FOR FIXED VALUE OF RL IN FIGURE THE VOLTAGE VI MUST BE SUFFICIENTLY TO TURN THE ZENER

DIODE ON. THE TURN ON VOLTAGE IS DETERMINED BY:

𝐼𝐿 =𝑉𝑍𝑅𝐿

(𝐶𝑜𝑛𝑠𝑡𝑎𝑛𝑡)

𝐼𝑆(𝑚𝑖𝑛) = 𝐼𝑍𝐾 + 𝐼𝐿

𝑉𝑖(𝑚𝑖𝑛) = 𝐼𝑆(𝑚𝑖𝑛)𝑅𝑆 + 𝑉𝑍

𝐼𝑆(𝑚𝑎𝑥) = 𝐼𝑍𝑀 + 𝐼𝐿

𝑉𝑖 𝑚𝑎𝑥 = 𝐼𝑆(𝑚𝑎𝑥)𝑅𝑆 + 𝑉𝑍

Example:

Determine the range of values of Vi that will maintain the Zener diode of

Figure in the “on” state.

Solution:

𝑉𝑖(𝑚𝑖𝑛) =(𝑅𝐿 + 𝑅𝑆)𝑉𝑍

𝑅𝐿=

1200 + 220 (20)

1200= 23.67 𝑉

𝐼𝐿 =𝑉𝐿𝑅𝐿

=𝑉𝑍𝑅𝐿

=20

1.2 𝑘Ω= 16.67 𝑚𝐴

𝐼𝑅(𝑚𝑎𝑥) = 𝐼𝑍𝑀 + 𝐼𝐿 = 60 + 16.67 = 76.67 𝑚𝐴

𝑉𝑖(𝑚𝑎𝑥) = 𝐼𝑅(𝑚𝑎𝑥)𝑅𝑆 + 𝑉𝑍 = 76.67 𝑚𝐴 0.22 𝑘Ω + 20

= 16.87 + 20 = 36.87 𝑉