the slope gives the forward resistance of the diode. ii) Reverse bias characteristics • In the reverse bias, the polarity of the DC power supply is reversed so that the P- region of the diode is connected to the negative terminal and N-region to the positive terminal of the DC power supply • The connections are made as given in the circuit diagram. • The voltage across the diode can be varied with the help of the variable DC power supply. • The reverse voltage ( V R ) across the diode is increased from V in steps of V up to V and the reverse current ( I R ) through the diode is noted from the micro-ammeter.
The readings are tabulated. • The reverse voltage V R and reverse current I R are taken as negative. • A graph is drawn taking the reverse bias voltage ( V R ) along negative x-axis and the reverse bias current ( I R ) along negative y-axis. Knee voltage Reverse bias Forward bias Slope ∆ = ∆ Forward resistance slope (µA) (mA) +V F (V) +I F –I R –V R (V) ∆ I F ∆ V F XII- - ) XII- - ) - - - - PRACTICAL OBSERVATION Table Forward bias characteristic curve S.No.
Forward bias voltage V F (volt) Forward bias current I F (mA) Table Reverse bias characteristic curve S.No. Reverse bias voltage V R (volt) Reverse bias current I R ( µ A) CALCULATION (i) Forward resistance R F = (ii) knee voltage = RESULT The V-I characteristics of the PN junction diode are studied. i) Knee voltage of the PN junction diode =………………V ii) Forward resistance of the diode =………………Ω Practical Tips • The DC power supply voltage should be increased only up to the specified range in the for- ward ( – 2V) and reverse ( – 15V) directions. Forward bias offers very low resistance and hence an external resistance of 470Ω is connected as a safety measure.