Class 12 Physics Lab Experiments

To draw the characteristics curves of a zener diode and to determine its reverse breakdown voltage

May 28 2023

Aim

To draw the characteristics curves of a zener diode and to determine its reverse breakdown voltage.

Apparatus

One p-n junction Zener diode, a power supply with potential divider (0-15V), a resistance of Ω , a micro ammeter of range (0-100 μA) , a voltmeter (0-15V), connecting wires.

Theory:

Zener diode: It is a semi conductor diode; in which n-type & p-type sections are heavily doped i.e. they have more percentage of impurity atoms. It results into low value of reverse breakdown votage (V _br). The reverse breakdown voltage of a zener diode is called zener voltage (Vz)- The reverse current that results after the breakdown is called zener current (I _Z).

Circuit Parameters:

V _I= Input (reverse bias) voltage V _o = Output voltage R _I = Input resistance, R _L= Load Resistance

Relation: I_L = I_I – I _z V _o = V _I- R _II _I V _o= R _II _I

S.No.	Input Voltage V _r= n x LC	Input Current I _r= n x LC (mA)
1	5 x 0.25 = 1.0	0
2	10 x 0.25 = 2.5	0
3	15 x 0.25 = 3.75	0
4	20 x 0.25 = 5	0
5	25 x 0.25 = 6.25	0
6	30 x 0.25 = 7.5	0
7	35 x 0.25 = 8.75	13 x 0.05 = 0.65
8	40 x 0.25 = 10	1.8
9	41 x 0.25 = 10.25	2.25
10	43 x 0.25 = 10.75	3

Initially as V _Iincreases, I increases a little.

At breakdown, increase of V _I increases I ₁by large amount.

So that V _o= V _I- R _II _I= constant

Observation:

Least count of voltmeter: 0.25 v/div Least count of milli ammeter: 0.05mA/div

Result:

From the graph of I _r vs V _r, the reverse breakdown voltage for the zener diode is 10.75V

Precautions:

The Zener diode p-n junction should be connected in reverse-bias i.e. p-terminal to –ve and to positive terminal of battery.
Zero error in the instruments should be adjusted in readings.
Voltmeter & ammeter of appropriate least counts should be used.