. VOLTAGE-CURRENT CHARACTERISTICS OF A ZENER DIODE AIM To draw the voltage-current (V-I) characteristic curves of a Zener diode and to determine its knee voltage, forward resistance and reverse breakdown voltage. APPARATUS REQUIRED Zener diode 1Z5.6V, variable dc power supply ( – 15V), milli ammeter, volt meter, Ω 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) Zener diode and its symbol (The black colour ring denotes the negative terminal of the Zener diode) Figure (b) Zener diode in forward bias mA ( - V) 1Z5.6V Figure (c) Zener diode in reverse bias mA ( - 15V) 1Z5.6V Precaution Care should be taken to connect the terminals of ammeter, voltmeter, dc power supply and the Zener 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-re- gion 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 .1V in steps of .1V up to .8V and the forward current ( I F ) through the diode is noted from the milli-ammeter.
The read- ings are tabulated. • The forward voltage and the forward current are taken as positive. • A graph is drawn taking the forward voltage along the x-axis and the forward current 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