electronics 1 - ceng.tu.edu.iq
TRANSCRIPT
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ELECTRONICS 1
Lecturer:
Yaroub Ghazi
1
Tikrit University
Electrical and Electronic Engineering Department
Second Year
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LECTURE 6: ZENER DIODE
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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
โGENERATEโ CARRIER. DIODE EMPLOYING THIS UNIQUE PORTION OF THE
CHARACTERISTIC OF A P-N JUNCTION ARE CALLED ZENER DIODES.
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ZENER DIODE
โข 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.
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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
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ZENER DIODE APPLICATIONS
B. SIMPLE SQUARE WAVE GENERATOR
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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.
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ZENER DIODE APPLICATIONS
3- DC VOLTAGE REGULATORS
A. FIXED VI, VARIABLE RL
๐ผ๐ =๐๐ โ ๐๐๐ ๐
(๐ถ๐๐๐ ๐ก๐๐๐ก)
๐ผ๐ฟ(MIN) = ๐ผ๐ โ ๐ผ๐๐
๐ ๐ฟ(๐๐๐ฅ) =๐๐
๐ผ๐ฟ(๐๐๐)
๐ผ๐ฟ(๐๐๐ฅ) = ๐ผ๐ โ ๐ผ๐๐พ
๐ ๐ฟ(๐๐๐) =๐๐
๐ผ๐ฟ(๐๐๐)
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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)
๐ ๐ฟ(๐๐๐) =๐ ๐๐๐๐๐ โ ๐๐
=(1 ๐ฮฉ)(10)
50 โ 10=
10 ๐ 103
40= 250 ฮฉ
๐๐ ๐ = ๐๐ โ ๐๐ = 50 โ 10 = 40 ๐
๐ผ๐ ๐ =๐๐ ๐ ๐ ๐
=40
1 ๐ฮฉ= 40 ๐๐ด
๐ผ๐ฟ(๐๐๐) = ๐ผ๐ ๐ โ ๐ผ๐๐ = 40 โ 32 = 8 ๐
๐ ๐ฟ(๐๐๐ฅ) =๐๐
๐ผ๐ฟ(๐๐๐)=
10
8 ๐๐ด= 1.25 ๐ฮฉ
(b)
๐๐๐๐ฅ = ๐๐๐ผ๐๐ = 10 32 ๐๐ด = 320 ๐๐
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B. FIXED RL, VARIABLE VI
โข 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:
๐ผ๐ฟ =๐๐๐ ๐ฟ
(๐ถ๐๐๐ ๐ก๐๐๐ก)
๐ผ๐(๐๐๐) = ๐ผ๐๐พ + ๐ผ๐ฟ
๐๐(๐๐๐) = ๐ผ๐(๐๐๐)๐ ๐ + ๐๐
๐ผ๐(๐๐๐ฅ) = ๐ผ๐๐ + ๐ผ๐ฟ
๐๐ ๐๐๐ฅ = ๐ผ๐(๐๐๐ฅ)๐ ๐ + ๐๐
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Example:
Determine the range of values of Vi that will maintain the Zener diode of
Figure in the โonโ state.
Solution:
๐๐(๐๐๐) =(๐ ๐ฟ + ๐ ๐)๐๐
๐ ๐ฟ=
1200 + 220 (20)
1200= 23.67 ๐
๐ผ๐ฟ =๐๐ฟ๐ ๐ฟ
=๐๐๐ ๐ฟ
=20
1.2 ๐ฮฉ= 16.67 ๐๐ด
๐ผ๐ (๐๐๐ฅ) = ๐ผ๐๐ + ๐ผ๐ฟ = 60 + 16.67 = 76.67 ๐๐ด
๐๐(๐๐๐ฅ) = ๐ผ๐ (๐๐๐ฅ)๐ ๐ + ๐๐ = 76.67 ๐๐ด 0.22 ๐ฮฉ + 20
= 16.87 + 20 = 36.87 ๐