Exp No: Date:DIODE RECOVERY CHARACTERISTICSAIM:

To study recovery characteristics of different types of diodes at two different forward currents.COMPONENTS AND APPARATUS:Serial NoITEMS DESCRIPTIONQUANTITY

1Signal generator1

2Diodes (Normal Recovery 1N4001) (Fast Recovery 1N5819,1N4148)1 each

3Resistances (47, 270), 1/3 W1 each

4Dual-trace Oscilloscope with isolation transformer 1

5Identical 1:1 probes2

THEORY:The familiar exponential i-v characteristic of the diffused junction p-n diode is an equilibrium relationship During the diode turn -off transient, its stored minority charge must be removed, either actively via negative current or passively by recombination inside the device. The diode remains forward biased while minority charge is present in the vicinity of the diode semiconductor junction. The initial amount of minority charge is a function of the forward current, and its rate of change, under forward- biased conditions. The turn off switching time is the time required to remove all this charge, and establish a new reverse-biased operating point when the diode is able to block the entire applied negative voltage. This process of switching the diode from the forward biased to reverse-biased states is called reverse recovery.

Fig 1 Circuit Diagram

PROCEDURE:-

The test set up is shown in Fig.1Set the signal generator open circuit output voltage to be a square pulse of amplitude 7.5V and frequency about 500Hz.. Set the output resistance of the signal generator to 50 to reduce the effect of loading of the signal generator. Make the connections as per the circuit diagram as shown in Figure (1) so that the forward current is of the required value say (20mA and 100mA). Supply the input to the dual trace oscilloscope through an isolation transformer. Observe the waveforms of voltage across the diode, current through the diode and the voltage applied to the circuit .Measure the reverse recovery time (trr) of the diode and the reverse recovery charge.Results/Observations1. The Voltage and current waveforms observed is shown in Fig. 2. (a) Reverse recovery time (trr) of the diode with the forward current of ------ is ----

(b) Reverse recovery time (trr) of the diode .with the forward current of ------ is ----3. (a) Reverse recovery charge of the diode with the forward current of ------ is ----

(b) Reverse recovery charge of the diode with the forward current of ------ is ----4. The forward voltage drop while carrying on state current of A ------- =

5. Voltage drop across the diode while minority stored charge is recovered ------ =

6. The time between the application of forward current and time when forward voltage equals the steady forward voltage if significant =

ComponentsMaximum MarksObtained

Marks

Prerequisite1

Viva2

Record (Hand Drawn circuit diagram and Model Graph)1

Conduction, Graph(Hand Drawn) & Results2

Inference2

Total8

Signal generator

Gnd

H2

H1