Power Electronics MTE-310 Lab#02 20-02-2020

Diode and its characteristics

Objective:
1. To study V-I characteristics of a diode.
2. To study the reverse recovery characteristics of power diode.

Apparatus:
 Function Generator
 Oscilloscope
 Diode
 Variable DC Power supply
 DMM
 Resistor

Theory
Diode:

Diode, an electrical component that allows the flow of current in only one direction. In circuit diagrams, a
diode is represented by a triangle with a line across one vertex.

The most common type of diode uses a p-n junction. In this type of diode, one material (n) in which
electrons are charge carriers abuts a second material (p) in which holes (places depleted of electrons that act
as positively charged particles) act as charge carriers. At their interface, a depletion region is formed across
which electrons diffuse to fill holes in the p-side. This stops the further flow of electrons. When this junction
is forward biased (that is, a positive voltage is applied to the p-side), electrons can easily move across the
junction to fill the holes, and a current flow through the diode. When the junction is reverse biased (that is, a
negative voltage is applied to the p-side), the depletion region widens and electrons cannot easily move
across. The current remains very small until a certain voltage (the breakdown voltage) is reached and the
current suddenly increases.

Forward Biasing:
When the voltage is applied in the opposite direction across the diode, the depletion region begins to shrink
(see Figure 3). In a reverse-biased diode, the electrons and holes would be pulled away from the junction,
but a forward-biased scenario ensures that the electrons and holes move toward the junction as they are
repelled from the positive and negative terminals of the voltage source respectively.

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Power Electronics MTE-310 Lab#02 20-02-2020
Reverse Biasing:
If a voltage is applied across the diode in such a way that the n-type half of the diode was connected to the
positive terminal of the voltage source and the p-type half was connected to the negative terminal, electrons
from the external circuit would create more negative ions in the p-type region by "filling the holes" and
more positive ions would be created in the n-type region as electrons are displaced toward the positive
terminal of the voltage source.

Reverse Recovery Time:

Reverse Recovery Time is the time it takes a diode to reduce the reverse current to zero when going
from forward bias to reverse bias. Contrary to popular opinion and idealized models’ diodes do conduct in
the reverse direction, but only for a short while.
A fast recovery diode has a smaller reverse recovery time than a standard diode.

Trr = Tp + Td
The ratio of these two-time factors (viz., t p and td) is known as the softness factor. In the case of a normal
diode, the time is taken by the current to decay (t d) will be smaller in comparison to the time taken by the
current to reach its negative peak (t p). On the other hand, for a soft recovery diode, the situation will be the
reverse. That is, here, td will be larger in comparison to tp. We can see that the softness factor gives a
measure of semiconductor losses incurred during switching. Greater is this ratio; greater will be the
switching loss. From this, one can conclude that when we use soft-recovery diodes, the losses experienced
by the semiconductor switching are more than those encountered when we use normal diodes.

Soft recovery:
Soft-Recovery Diode Boosts Power-Factor Correction. A series of hyper fast soft-recovery
diodes has been released by International Rectifier. To reduce conduction and switching losses, these
rectifiers offer low forward-voltage drop and reverse leakage current.

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Power Electronics MTE-310 Lab#02 20-02-2020
Abrupt recovery:
When the voltage across a diode is suddenly reversed, an initial current flow will occur in
the reverse direction. Reverse recovery time is the time taken to stop conducting when
the diode is reverse biased.

Table:
Forward Biasing Reverse Biasing
Forward Forward Reverse Reverse
Input Voltage Input Voltage
Sr No. Voltage Current Voltage Current
(V) (V)
(V) (mA) (V) (uA)
1 0 0 0 0 0 0
2 0.25 0.25 0 1.32 1.32 0
3 0.43 0.35 0 3.58 3.58 0
4 0.95 0.49 0.7 7.71 7.71 0
5 1.24 0.51 0.8 12.5 12.5 0
6 2.5 0.55 2.08 15.9 15,9 1
7 3.24 0.56 2.43 20.3 20.3 1
8 3.63 0.57 3.12 26.5 26.5 2
9 4.31 0.58 3.78 28 28 2
Graph:

Forward Biasing
5
Input Voltage Forward Voltage Forward Current
4.5 4.31

4 3.78
3.63
3.5 3.24
3.12
3
2.5 2.43
2.5
2.08
2

1.5 1.24
0.95
1 0.7 0.8
0.49 0.51 0.55 0.56 0.57 0.58
0.43
0.35
0.5 0.25
0 0 0
0
0.5 1 1.5 2 2.5 3 3.5 4 4.5

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Power Electronics MTE-310 Lab#02 20-02-2020

Reverse Biasing
30
28
Input Voltage(V) Reverse Voltage(V) Reverse Current(uA) 26.5
25

20.3
20

15.9
15
12.5

10
7.71

5 3.58
1.32 2 2
1 1
0 0 0 0 0
0
1 2 3 4 5 6 7 8 9

Circuit Diagram:

• At frequency= 1KHz, Amplitude= 5V, Load= 1Kohm

• when freq= 2KHz, amplitude= 5V, load = 1K ohm

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Power Electronics MTE-310 Lab#02 20-02-2020
• when Freq= 5kHz, amplitude= 5V, Load= 1Kohm

• Freq = 2Hz, Amplitude=9V, load= 1k ohm

• Freq= 2kHz, Amplitude= 22V, load=1K ohm

• Freq= 4KHz, amplitude= 5V Load=571.42ohm

• Req= 1/[(1/1k)+(1/2k)+(1/4k)]
• Req=1/(1k+0.5k+0.25k)
• Req=1/1.75k
• Req= 0.57142k ohm Req=571.42ohm

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Power Electronics MTE-310 Lab#02 20-02-2020

PROCDURE:
1) First of all, we patch a circuit of forward biasing by using a diode and a load resistor.
2) The diode Anode terminal is connected with the positive terminal of the power supply.
3) The negative terminal of the power supply is connected with the load resistor. The diode and the load
resistor are connected in series.
4) Then we set input voltage at 0.25v and checked by DMM. Then we check forward voltage across the
diode. After that we checked the forward current across the diode by using DMM.
5) Repeat the experiment 8 times for different input voltage levels.
6) First of all, we patch a circuit of Reverse biasing by using a diode and a load resistor.
7) The diode Anode terminal is connected with the Negative terminal of the power supply.
8) The positive terminal of the power supply is connected with the load resistor. The diode and the load
resistor are connected in series.
9) Then we set input voltage at 1.32v and checked by DMM. Then we check Reverse voltage across the
diode. After that we checked the reverse current across the diode by using DMM.
10) Repeat the experiment 8 times for different input voltage levels.
11) After that we patched a third circuit for reverse recovery time the load resistor and diode are in series
and we apply a AC power source.
12) At first, the value of load resistor is fixed (1k). We varied the value of Amplitude to analyze the
waveform at different levels.
13) Then we fixed the value of Frequency (2KHz). and we varied the value of resistor to analyze the
waveform at different levels.

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Power Electronics MTE-310 Lab#02 20-02-2020

Conclusion:
In this lab we learned about the forward biasing and reverse biasing. We learnt about the working of
diode and we learnt that what is the effect of load resistor when connected in series. We learnt about the
reverse recovery time and we analyze reverse recovery time with the help of different waveforms.

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