JUNCTION DIODE AIM To draw the voltage-current (V- I) characteristics of the PN junction diode and to determine its knee voltage and forward resistance. APPARATUS REQUIRED PN junction diode (IN4007), variable DC power supply, milli-ammeter, micro-ammeter, voltmeter, resistance and connecting wires. FORMULA = ∆ ∆ (Ω) where, R F → Forward resistance of the diode (Ω) ∆ V F ® The change in forward voltage (volt) ∆ I F ® The change in forward current (mA) CIRCUIT DIAGRAM Figure (a) PN junction diode and its symbol (Silver ring denotes the negative terminal of the diode) Figure (b) PN junction diode in forward bias mA ( - V) IN4007 Figure (c) PN junction diode in reverse bias µA ( - V) IN4007 Precaution Care should be taken to connect the terminals of ammeter, voltmeter, dc power supply and the PN junction diode with right polarity. XII- - ) XII- - ) - - - - PRACTICAL PROCEDURE i) Forward bias characteristics • In the forward bias, the P- region of the diode is connected to the positive terminal and N-region to the negative terminal of the DC power supply.
• The connections are given as per the circuit diagram. • The voltage across the diode can be varied with the help of the variable DC power supply. • The forward voltage ( V F ) across the diode is increased from . V in steps of .
V up to . V and the forward current ( I F ) through the diode is noted from the milli-ammeter. The readings are tabulated. • The forward voltage V F and the forward current I F are taken as positive.
• A graph is drawn taking the forward voltage ( V F ) along the x-axis and the forward current ( I F ) along the y-axis. • The voltage corresponding to the dotted line in the forward characteristics gives the knee voltage or threshold voltage or turn-on voltage of the diode. • The slope in the linear portion of the forward characteristics is calculated. The reciprocal of