A Zener diode is a type of diode that permits current not only in the forward direction like a normal diode, but also in the reverse direction if the voltage is larger than the breakdown voltage known as “Zener knee voltage” or “Zener voltage”.
The device is named after American physicist Clarence Melvin Zener, who first described the ZENER EFFECT in1934. Later his work led to the BELL LABS implantation of the effect in form of an electronic device, the ZENER DIODE.
Zener diodes are a modified form of PN silicon diode used extensively for voltage regulation. The P type and N type silicon used is doped more heavily than a standard PN diode.
This causes a very thin depletion region. The zener diodes breakdown characteristics are determined by the doping process
Zeners are commercially available with voltage breakdowns of 1.8 V to 200 V.
When a Zener diode is forward biased, it operates as a normal diode.
In forward biased P side connected to positive and N side connected to negative terminal of battery. In this case the electrons and holes are swept across the junction and large current flow through it.
In case of reverse biased current practically zero and at certain voltage which called Zener voltage the current increases sharply.
Each Zener diode has breakdown rating which specifies the max voltage that can be dropped across it.
Zener diodes are designed to operate in reverse breakdown. Two types of reverse breakdown in a zener diode are AVALANCHE and ZENER. The avalanche break down occurs in both rectifier and zener diodes at a sufficiently high reverse voltage. Zener breakdown occurs in a zener diode at low reverse voltages.
A Zener allows current to flow in the reverse direction when the voltage is above a certain value known as the breakdown voltage, "Zener knee voltage", "Zener voltage", “Avalanche point", or “Peak inverse voltage”
Breakdown Characteristics : Figure 2 shows the reverse portion of a zener diode’s characteristic curve. As the reverse voltage (푉_푅 ) is increased, the reverse current (퐼_푅 ) remains extremely small up to the “knee” of the curve. The reverse current is also called the zener current, 퐼_푍 . At this point, the breakdown effect begins; the internal zener resistance, also called zener impedance (푍_푍), begins to decrease as reverse current increases rapidly.Voltage Regulator :In a DC circuit, Zener diode can be used as a voltage regulator to regulate the voltage across small circuits.
Waveform Clipper :Zener diode can be used to make a Waveform Clipper. Two Zener diodes facing each other in series will act to clip both halves of an input signal.
Voltage Shifter :A Zener diode can be applied to a circuit with a resistor to act as a voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the Zener diode's breakdown voltage.
3. WHAT IS ZENER DIODE ?
A Zener diode is a type of diode that permits current not only in the
forward direction like a normal diode, but also in the reverse direction if
the voltage is larger than the breakdown voltage known as “Zener knee
voltage” or “Zener voltage”.
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(1905 –1993)
The device is named after American physicist Clarence Melvin Zener, who
first described the ZENER EFFECT in1934. Later his work led to the BELL LABS
implantation of the effect in form of an electronic device, the ZENER DIODE.
4. CONSTRUCTION OF ZENER DIODE
This causes a very thin depletion region. The zener diodes breakdown characteristics are determined by the doping process
Zeners are commercially available with voltage breakdowns of 1.8 V to 200 V.
Zener diodes are a modified form of PN silicon diode used extensively for voltage regulation. The P type and N type
silicon used is doped more heavily than a standard PN diode.
CONSTRUCTION OF ZENER DIODE
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5. 5
FORWARD BIASING
When a Zener diode is forward biased, it operates as a normal diode.
In forward biased P side connected to positive and N side connected to negative terminal of
battery. In this case the electrons and holes are swept across the junction and large current
flow through it.
WORKING OF ZENER DIODE
(BIASING)
REVERSE BIASING
In case of reverse biased current practically zero and at certain voltage which called Zener
voltage the current increases sharply.
Each Zener diode has breakdown rating which specifies the max voltage that can be
dropped across it.
Reverse bias of Zener Diode
Forward bias of Zener Diode
6. 6
ZENER BREAKDOWN VOLTAGE
A Zener allows current to flow in the reverse direction when the voltage is above a certain value
known as the breakdown voltage, "Zener knee voltage", "Zener voltage", “Avalanche point", or
“Peak inverse voltage”
Breakdown Characteristics : Figure 2 shows the reverse portion of a zener diode’s characteristic
curve. As the reverse voltage (𝑉𝑅 ) is increased, the reverse current (𝐼 𝑅 ) remains extremely
small up to the “knee” of the curve. The reverse current is also called the zener current, 𝐼 𝑍 . At
this point, the breakdown effect begins; the internal zener resistance, also called zener
impedance (𝑍 𝑍), begins to decrease as reverse current increases rapidly.
Zener diodes are designed to operate in reverse breakdown. Two types of reverse breakdown in a zener diode are AVALANCHE
and ZENER. The avalanche break down occurs in both rectifier and zener diodes at a sufficiently high reverse voltage. Zener
breakdown occurs in a zener diode at low reverse voltages.
FIGURE 01
FIGURE 02
7. 7
ZENER DIODE APPLICATION
Voltage Regulator :In a DC circuit, Zener diode can be used as a voltage regulator to
regulate the voltage across small circuits.
Waveform Clipper :Zener diode can be used to make a Waveform Clipper. Two Zener diodes
facing each other in series will act to clip both halves of an input signal.
Voltage Shifter :A Zener diode can be applied to a circuit with a resistor to act as a
voltage shifter. This circuit lowers the output voltage by a quantity that is equal to the
Zener diode's breakdown voltage.
Voltage Regulator’s Circuit
Waveform Clipper’s Circuit
Voltage Shifter‘s Circuit
