calculated. The reciprocal of 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 .5V in steps of .5V up to 6V and the reverse current ( I R ) through the diode is noted from the milli-ammeter. The readings are tabulated. • Initially, the voltage is increased in steps of .5V. When the breakdown region is approxi- mately reached, then the input voltage may be raised in steps of, say .1V to find the break- down voltage.
• The reverse voltage and reverse current are taken as negative. • A graph is drawn taking the reverse bias voltage along negative x-axis and the reverse bias current along negative y-axis. • In the reverse bias, Zener breakdown occurs at a particular voltage called Zener voltage V Z (~ . to .8V) and a large amount of current flows through the diode which is the character- istics of a Zener diode.
• The breakdown voltage of the Zener diode is determined from the graph as shown. XII- - ) XII- - ) - - - - PRACTICAL Zener Breakdown Region Forward Bias Region Zener breakdown voltage Slope ∆ = ∆ Forward resistance slope Knee voltage -V Z ∆ I F ∆ V F (µA) +V F (V) +I F –V R (V) (mA) –I R 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 (mA) CALCULATION (i) Forward