diode characterization

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International Journal of Advances in Electrical and Electronics Engineering 30

ISSN: 2319-1112

ISSN:2319-1112 /V1N1:30-36 IJAEEE

Power efficiency of diode

(calculation of various resistances)Shashiketan Samal

1, Rama komargiri

2,Kotni Siddharth

3

Department of Electronics and communication Engineering1 3

Student, ISM Dhanbad2Asst. Prof. NIT Calicut

[email protected]

ABSTRACT-The day-to-day life is becoming much faster and hectic. So, there is a long quest between power

consumption and reducing the cost of a device. Hence, in this long run using a particular device efficiently

comes into the field. A simple diode can be much more useful to us if used at a particular voltage considering

the resistances associated with it. This problem is being solved using the simulations of PN junctions with

varying widths. The calculation of series resistance and high level injection resistance gives a brief idea aboutthe resistance associated with the diode. Variation of its nature with voltage and current can be very useful to

calculate the working voltage of a diode.

Keywords-pn junction; diode; power efficiency; series resistance; high level injection resistance; junction

resistance

I. Introduction

Indeed, the diode is the simplest element of electronics. Analyzing the diode in a circuit containing voltage source, It

has been found that the current across the diode increases with increase in applied voltage. This suggests that diode

has certain resistance attached to it. From the theory it is determined that at very high voltage a process called high

level injection occurs which adds to the resistance of diode. Hence a diode can be thought of attached with three

types of resistances:

Series resistance Junction resistance High level injection resistance.

The series resistance can be approximated to be equal on both sides of P and N junctions for equal doping

concentrations. This resistance is negligible for lower width of PN junctions.Hence an analysis has been done to calculate the high level injection resistance and the series resistance of

the diode.

There is a small difference between the voltage applied and voltage across the diode. is the voltage across the

depletion region formed in the diode and this is the value used in the Shockley equation in (1)

(1)

Where, I- diode current

- Saturation current

- Voltage across diode


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31Power efficiency of diode (calculation of various resistances)

ISSN:2319-1112 /V1N1:30-36 IJAEEE

n- Ideality factor

-thermal voltage

A. calculating high level injection resistance

Increasing the voltage, a condition appears when the injected minority carrier densities become comparable to

majority carrier densities and a substantial portion of the applied bias drops across the region outside the depletion

region which itself shrinks. This is high level injection. The diode shows a peculiar behavior at this level in

consideration to resistance called high level injection resistance.

To calculate the high level injection resistance a PN junction of lower thickness (1 ) was used so as to neglect

the effect of series resistance. The simulations done are based on quantum mechanical model on Medici.

The doping concentrations were taken to be on both sides of junctions. The on voltage of diode has been

calculated as

(2)

Where, - cut off voltage

k- Boltzmann constant-

T- temperature-273K

q- charge of electron

- acceptor ions

- donor ions

free electrons

The cut-off voltage was found to be 0.575 volts.

The saturation nature of I-V characteristics of diode has been approximated using (1).

The value of ideality factor, n has been found to be around 2.18 in the linear region next to cut in voltage. Its growthis very rapid in the subsequent voltages.

Hence, the voltage across the diode could be calculated for a particular current value flowing in the circuit due to

the applied voltage. A brief comparison has been provided for V-I characteristics of diode using simulation through

Medici and through Shockley equation as shown in figure.1

Figure.1: Comparison of characteristics of ideal diode and practical diode through simulations on MEDICI


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IJAEEE ,Volume1,Number 1Shashiketan Samal et al.

ISSN:2319-1112 /V1N1:30-36 IJAEEE

Using Kirchhoffs voltage rule in a circuit shown in figure.2.we have,

Figure.2: A circuit showing application of voltage to diode

(3)

Where, - Voltage applied

- Voltage across Diode

- Diode current

- High level injection resistance

The applied voltage gets distributed in to the diode voltage and some part is lost in high level injection resistance.

Findings:

It has been observed that with increase in applied voltage the voltage across the diode increases very

sluggishly after the cut in voltage and remains to be around cut in voltage and becomes constant afterwards. This is

because a voltage barrier is formed due to the depletion region.

The variation of high level injection resistance with applied voltage and current has been studied and graphs are

plotted accordingly in figure.3.

Figure.3.(i): Variation of high level injection resistance with voltage

As this resistance is entirely due to high level injection, so there should be a minimum voltage where this

high level injection occurs. It has been justified to be the cut-in voltage as resistance values below this voltage are

absurd.

The high level injection resistance is found to increase linearly with applied voltage. As at high voltages current

saturates so the slope of voltage and high level injection resistance remains constant. The minimum value of the

resistance can be approximated due to the series resistance.

The variation of this resistance with current flowing in the circuit is shown in fig 3.(ii).

There is a parabolic increase in resistance with current flowing in the circuit.


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ISSN:2319-1112 /V1N1:30-36 IJAEEE

Figure.3.(ii): Variation of high level injection resistance with current

B. calculating series resistanceThe series resistance is contributed due to varying width of p-n junction. As the doping concentration is considered

same on both sides so resistance considered is equal. The high level injection resistance has been calculated and it

becomes easier to calculate the series resistance of a diode. Hence a PN junction of larger width (3 ) and doping

concentrations (same as before) has been used.

It has been observed that:

Increasing the doping of P and N junctions, the current saturates at a higher value. This indicates thedecreased level of resistance. This phenomenon is because of increase in number of carriers of holes and

electrons.

Decreasing the doping of junctions saturates the current much earlier. Hence the high level injectionresistance could be neglected in such cases and the resistance can be assumed completely due to the series

and junction resistance.

Hence, the doping level is chosen accordingly so as to include the effect of high level injection resistance.

The series resistance is calculated using (4). Using Kirchhoffs voltage rule in the circuit as shown in fig.2 and

accounting for high level injection resistance, so

(4)

Where - series resistance

The effect of voltage across the diode and high level injection resistance is used to calculate the series the

resistance.

Figure.1 is used to calculate the voltage across the diode for a applied voltage and 2nd

degree interpolation is

used for calculating high level injection resistance

findings:

The variation of series resistance with applied voltage has been plotted below:


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ISSN:2319-1112 /V1N1:30-36 IJAEEE

Figure.4.(i): Variation of series resistance with voltage

The series resistance is observed to be constant in the region near the bias voltages. Initially, the series

resistance is high indicating negligible current through the circuit. The resistance is found to increase linearly

after a particular voltage. This may be due to the increase in number of carriers or combination with high levelinjection resistance.

The variation of series resistance with current flowing in the circuit is found to be similar with the above

behavior as shown below:

Figure.4.(ii): Variation of series resistance with current

The resistance increase parabolically after a limiting current in the circuit. Till then the resistance varies sluggishly.

C. junction resistance

As the p and n junctions which have large concentration of holes and electrons are joined, the diffusion of carrier

takes place at the junction due to concentration gradient. In equilibrium the ionized region consisting of positive and

negative charges is called depletion. This gives rise to an electric field and thus electric potential. This built in

potential opposes the flow of majority carriers.

Hence, they are said to face a resistance which appears across the junction i.e. across the depletion region called

junction resistance. This resistance is very high which doesnt allow any current to flow in the circuit initially till the

cutoff voltage given by (2). The variation of built in potential with application of voltage is shown in fig 4.


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Figure.5: Variation of built in potential with applied voltage

The junction potential reaches a constant value swiftly and hence junction resistance is assumed to be of constant

high value.

II. inference

Hence, every diode is associated with three types of resistance- high level injection resistance and series

resistance depending upon the voltages applied. At lower voltages, apart from junction resistance series

resistance dominates which is nearly constant. So, current increases rapidly. As the applied voltage increases,

series resistance and high level injection resistance start increasing linearly although junction resistance is

constant and hence the current saturates at a particular value as justified by the simulations.

Hence while using diode for practical applications in life; special considerations need to be taken for

resistance of diode and voltage being applied to it. To derive maximum power output from the diode the

external resistance should be made equal to the variable diode resistance.

For maximum power output, only increase in voltage wont serve the purpose because after a particular voltagevalue (as observed) the increase in power output is very minimal as shown in the fig.6

Figure.6: Variation of output power with applied voltage

After 2.1 Volts, increase in power output is very less hence this diode should be appropriately used at that

voltage for its aptness.


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ISSN:2319-1112 /V1N1:30-36 IJAEEE

III. Conclusion

A diode can be used meticulously and properly if we change the junctions from PN to P+ N. and hence, for its

maximum power output it should be operated at a particular voltage taking resistance (High level injection and

series) into considerations.

IV. ACKNOWLEDGMENT

I would like to express my deep sense of gratitudeto our Professor Dr. Rama Komaragiri, Department of ECE, NIT

Calicut for providing us such a great opportunity to work under him.We would like to thank Dr. P.S. Sathidevi,

HOD, ECED, NITCalicut for her support and providing us the facilities.

V. REFERENCES

[1] Semiconductor optoelectronic Devices Pallab Bhattacharya.[2] Robertboylestad, Louis nashelsky Electronic Devices and Circuit Theory

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diode characterization