Lecture No# 2 Prepared by: Engr. Qurban Ali Memon Incharge of Final Project Lab.

Introduction to diode: The diode was been invented in the year 1950. The diode is a device which current flows only one direction. The diode has two terminals. Two terminals are anode (A) and cathode (K). The anode has positive charge and cathode negative charge. The diode decides whether condition is forward bias or reverse bias. The potential barrier of silicon is 0.7v and germanium 0.3v. The diode is used for rectification. A K

In forward bias In reverse bias

To test the diode by using Multimeter Lab # 01 To test the diode by using Multimeter Components: 1. 1N4001 2. Multimeter .3 Brad board To check the resistance of diode on both ways. If you get zero resistance on both ways, the diode is shorted. If you get INFINITY resistance on both ways, the diode is open. If you get some resistance on one way (forward)but INFINITY or high on the other way (reverse) then the diode is good.

To check the Resistance of diode in forward bias. Set the multimeter meter on low scale, say 20K. Now connect the positive lead of multimeter on anode of the diode (the black part of the diode and the negative probe on the cathode of the diode (the silver strip), as shown below. If the multimeterr shows the very low resistance, maybe few kilo ohm. This a check for condition of diode in forward bias.

To check the Resistance of diode in reverse bias. Set the multimeter meter on high scale, say 200M or above. Now connect the positive lead of multimeter with anode and negative lead of multimeter with cathode. If the multimeter show the very high resistance above 10M or infinity.  This a check for condition of diode in reverse bias.

LAB EXPERIMENT NO # 02 To understand the Voltage – Current characteristics of a junction diode by using (a) Kit (b) Breadboard Components: 1. Kit 2. Diode 3. Voltmeter 4. Milliameter 5. Resistor 6. d.c supply 7. Few connecting leads

There are two operating regions and three possible “biasing” conditions for the standard Junction Diode and these are: 1. Zero Bias : No external voltage potential is applied to the PN junction diode. 2. Reverse Bias: The voltage potential is connected negative, (-ve) to the P-type material and positive, (+ve) to the N-type material across the diode which has the effect of Increasing the PN junction diode’s width. 3. Forward Bias : The voltage potential is connected positive, (+ve) to the P-type material and negative, (-ve) to the N-type material across the diode which has the effect of Decreasing the PN junction diodes width.

1: Zero Biased Junction Diode When a diode is connected in a Zero Bias condition, no external potential energy is applied to the PN junction. However if the diodes terminals are shorted together. Initially when the forward bias voltage is zero, the current through the diode is also zero. The current through the diode is zero because there is no voltage applied across its terminals which could establish current.

2: Reverse Biased PN Junction Diode When a  Reverse bias condition, a positive terminal of battery or source is connected with cathode and a negative terminal of battery or source is connected with anode. In reverse bias the potential barrier is increased and does not current flow in circuit.

Forward Bias

3: Forward Biased PN Junction Diode When a  Forward Bias condition, a positive terminal of battery or source is connected with anode negative terminal of battery or source is connected with cathode. If this external voltage becomes greater than the value of the potential barrier, approx. 0.7 volts for silicon and 0.3 volts for germanium then current will start to flow.

V-I Characteristic of diode:-

Negative charge on P-side then holes to cross from P-side to N-side. Potential Barrier Positive charge on N-side then free electrons to cross from N-side to P-side. Negative charge on P-side then holes to cross from P-side to N-side.

Depletion Layer Positive charge on N-side then free electrons to move from N-side to P-side. The Result is that depletion layer is formed. No electros are left N-side