Class 12 Physics practical reading To draw the characteristic curve of a zener diode & to determine its reverse breakdown voltage.

Aim

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

Apparatus Required

A Zener diode, a high resistance rheostat, variable d.c. supply, a voltmeter, a multi-range ammeter, a resistance, a one-way key, and connecting wires.

Theory

Zener Diode 

If the reverse bias voltage across a p-n junction diode is increased, at a particular voltage called breakdown voltage, the (reverse) current suddenly increases to a large value which may even damage the diode. The Zener diode is specially made junction diode for use in reverse breakdown region which can be used continuously without being damaged. The breakdown voltage in a Zener diode is called the Zener voltage.

Procedure

Note the type and number of the Zener diode. Note its breakdown voltage, maximum current and wattage ratings. 

1. Make the connections as shown in the circuit diagram ensuring that they are neat and tight. Ensure that the positive terminals of voltmeter and ammeter are connected to the positive terminal of the battery.

2. Note the least count and zero error in the voltmeter and microammeter.
3. Adjust the rheostat to have minimum potential and insert the plug in key K to switch on the supply.
4. Gradually increase the potential difference across the diode by adjusting the rheostat in small steps and record the voltmeter reading and the current.  

5. At a certain potential difference across the diode, there is a sudden increase in the current. The voltage at which this happens is the reverse breakdown voltage of the diode. This voltage is also called zener diode. Record this voltage. 

6. Plot a graph between reverse voltage (V) along X'-axis and the current (I) along Y'-axis.

Observations

 

 

Precautions

1. The ends of the connecting wire should be cleaned with a sand paper and the connections should be neat and tight. 

2. The negative terminal of the power supply should be connected to the p-terminal and positive to the n-terminal of the zener diode so that the diode is reverse biased. 

3. The voltage should be increased gradually. 

4. The voltmeter should be connected in parallel and the multi-range ammeter in series.