Aim
To draw the characteristic curve of a Zener diode and to determine its reverse breakdown voltage.
Materials Required
- One 0-100 mA ammeter
- One 20 Ω resistance
- High resistance rheostat
- One Zener diode (reverse breakdown voltage value of around six volts (Vz = 6 V))
- Ten-volt battery
- One-way key
- Connecting wire
- Two 0-10 V voltmeter
Theory
Typically, a Zener diode is a type of semiconductor in which the p-type and the n-type parts are heavily doped. In other words, it has a higher percentage of impurity atoms. The doping produces a low reverse breakdown voltage. This breakdown value can be regulated during production. Zener voltage (V<sub>z</sub>) is the Zener diode’s reverse breakdown voltage. The reverse current that is produced prior to the breakdown is known as Zener current (I<sub>z</sub>).
Circuit Parameters
In the given circuit,
- VI = Input reverse bias voltage
- RI = Input resistance
- RL = Load resistance
- II = Input current
- V0 = Output voltage (RL/IL)
- IZ = Zener diode current
- IL = Load current
Equations
V0 = VI – RIII
V0 = VI – RIII
At breakdown, value of VI rises II by a large value, in a way that V0 = VI – RI II turns into a constant. This constant quantity V0 is the reverse breakdown voltage, which is also known as the Zener voltage.
Equations
V0 = VI – RIII
Constant value of V<sub>0</sub> shares reverse breakdown voltage.
Diagram
Precautions
All connections should be clean, tight, and neat. The key should be used in the circuit and opened when the circuit is not activated.
Procedure
- Organise the apparatus as displayed in the circuit diagram.
- Note down the zero error and the least count of milli-ammeters (micro-ammeters) and voltmeters.
- Place the moving rheostat or potential divider close to the negative terminal and slide the key (K). Milli-ammeter and voltmeters will show zero reading.
- Displace the contact marginally towards the positive terminal to give reverse bias voltage (VI). The milli-ammeter value will stay at zero. Voltmeters will give equivalent readings. V0 = VI …. II = 0
- When VI increases, then II will start flowing. Now, V0 will become lesser than VI. Write down the measurements of Vp II and V0.
- Increase VI in tiny increments of 0.5 V. Write down the corresponding value of V0 and II which will also be increased.
- When VI is raised furthermore, V0 and II will also be increased correspondingly.
- At one point, when VI is increased additionally, V0 will not increase and II will increase by a large amount.
- When VI is increased furthermore, only II will increase and V0 will become a constant. Write down values of II, VI, and VI.
- Rise V1 to a reading of 10 V, writing down the corresponding values.
Observation
Voltmeter zero error (V1) = ……. V
Voltmeter least count (V1) = …….. V
Voltmeter zero error(V2) = ……. V
Voltmeter least count (V2) = ……. V
Milli-ammeter zero error= ……. mA
Milli-ammeter least count = ……. mA
Table for VI, II and V0
|
Serial No. (1) |
Input voltage (V<sub>I</sub>) (2) |
Input current (I<sub>I</sub>) (µ) (3) |
Output Voltage V<sub>0</sub> (V) (4) |
|
a. b. c. d. . . . . . |
…… …… …… …… |
…… …… …… …… |
…… …… …… …… |
Calculations
Create a graph with input voltage VI and input current, representing VI on the X-axis and II on the Y-axis.
Result
The reverse breakdown voltage of this Zener diode is ……
Viva Voce
1. Define minority carriers?
Answer: Minority carriers are the free electrons existing inside p-type semiconductors and holes inside n-type semiconductors. They exist due to the disintegration of their covalent bonds.
2. What is meant by reverse breakdown and Zener effect?
Answer: In a particular case of expanding reverse bias voltage reading, the resulting reverse current rises abruptly. This process is known as the reverse breakdown, and the effect is called the Zener effect.
3. What is meant by reverse breakdown voltage?
Answer: The reverse breakdown voltage is caused by avalanche breakdown or Zener breakdown. In the case of a reverse-biased p-n junction, a depletion layer is extended along the p-n junction. It is denoted by the symbol BVR.
4. What is the factor that the reverse breakdown voltage relies on?
Answer: It relies upon the extent of doping of the n-type and the p-type parts in the diode.
Typical diodes have individual parts slightly doped. These diodes have a high reverse breakdown voltage. Zener diodes possess highly doped sections. They also possess low reverse breakdown voltage.
5. What is the Zener voltage variation between Silicon and Germanium?
Answer: In the case of the exact doping order, it is high for Silicon and relatively low for Germanium.
6. ________ is the reverse current generated after the breakdown. It is denoted by the symbol ________.
Answer: Zener current and I<sub>z</sub>
7. How do Zener diodes function as voltage regulators?
Answer: At and after the breakdown stage, output voltage (V0) changes into a constant at the Zener voltage (Vz) even if the input voltage (VI) rises. Therefore, this diode gives the identical output voltage in the case of all input voltages of greater values. It transforms into a voltage stabiliser for the equivalent voltage measurement of Zener voltage. The current generated will not have any effect on the existing Zener voltage.
8. What occurs in the depletion layer and potential barrier when a strong reverse bias is exerted on a p-n diode?
Answer: The depletion layer and potential barrier increase considerably.
9. Give an example for the application of a diode.
Answer: The rectifier is an application of a diode.
10. How does the energy gap vary with doping temperature?
Answer: The energy gap decreases with the increase in doping and temperature.
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