To Draw The Characteristic Curve Of A Zener Diode And To Determine Its Reverse Breakdown Voltage. - Practice Questions & MCQ

Aim-

To draw the characteristic curve of a Zener diode and to determine its reverse breakdown voltage.

Apparatus-

A Zener diode (with small reverse breakdown voltage of about 6 volts ), [i.e., $V_z=6 \mathrm{~V}_{\text {] }}$, a ten-volt battery, a high resistance rheostat, two $0-10 \mathrm{~V}$ voltmeter, one $0-100 \mathrm{~A}$ ammeter, one $20 \Omega$. resistance, one-way key, connecting wires.

Theory-
Zener Diode- It is a semiconductor diode, in which the n-type and the p-type sections are heavily doped, i.e., they have more percentage of impurity atoms. This heavy doping results in a low value of reverse breakdown voltage $\left(B V_R\right)$. This value can be controlled during manufacture. The reverse breakdown voltage of a Zener diode, is called Zener voltage $V_Z$.

The reverse current that results after the breakdown, is called Zener current $\left(I_z\right)$.
Circuit Parameters
In the circuit given before. $V_I=$ Input (reverse bias) voltage $V_0=$ Output voltage $\left(R_L / I_L\right)$
$R_I=$ Input resistance $R_L=$ Load resistance
$I_I=$ Input current (reverse current)
$I_Z=$ Zener diode current
$I_L=$ Load current
Relations

$
\begin{gathered}
I_L=I_I-I_Z \\
V_0=V_I-R_I I_I
\end{gathered}
$

Initially as $V_I$ is increased, $I_I$ increases a little, then $V_0$ increases.
At breakdown, increase of $V_I$ increases $I_I$ by a large amount, so that $V_0=V_I-R_I I_I$ becomes constant. This constant value of $V_0$ which is the reverse breakdown voltage is called Zener voltage.

Formula used

$
V_0=V_I-R_I I_I
$

The constant value of $V_0$ gives reverse breakdown voltage.

Diagram-

 Procedure
1. Arrange apparatus as shown in the circuit diagram.
2. Make all connections neat, clean and tight.
3. Note the least count and zero error of voltmeters and milli-ammeter. (micro-ammeter)
4. Bring moving contact of the potential divider (rheostat) near the negative end and insert the key K. Voltmeters and milli-ammeter will give zero reading.

5. Move the contact a little towards a positive end to apply some reverse bias voltage $\left(\mathrm{V}_{\mathrm{I}}\right)$. Milli-ammeter reading remains zero. Voltmeters give equal readings.

$
\left[\text { i.e, } \quad \mathrm{V}_0=\mathrm{V}_I \ldots \Rightarrow \mathrm{I}_I=0\right]
$

6. As $V_I$ is further increased, $I_I$ starts flowing. Then $V_0$ becomes less than $V_I$,

Note the values of $V_p \quad I_I$ and $\mathrm{V}_0$
7. Go on increasing $V_I$ in small steps of ). 5 V .

Note corresponding values of $\mathrm{I}_I$ and $\mathrm{V}_0$ which will be found to have increased.
8. As $V_I$ is made more and more, $I_I$ and $\mathrm{V}_0$ are found to increase. Values are noted.
9. At one stage, as $V_I$ is increased further, $I_I$ increases by a large amount and $\mathrm{V}_0$ does not increase. This is reverse breakdown situation.
10. As $V_I$ is increased further, only $I_I$ is found to increase, $\mathrm{V}_0$ becomes constant.

Note values of $V_I I_I$ and $\mathrm{V}_0$
11. Increase $V_I$ to a value of 10 V , noting corresponding values.
12. Record your observations .

Calculations-
Plot a graph between input voltage $V_I$ and input current $\left(I_I\right)$, taking $V_I$ along X -axis and $I_I$ along Y -axis.
Result-
The reverse'breakdown voltage of given Zener diode is....