Advertisements
Advertisements
प्रश्न
Explain the working of P-N junction diode in forward and reverse biased mode.
Advertisements
उत्तर
If a germanium crystal or silicon crystal is doped during manufacture in such a way that half of it is p-type and other half is n-type, we get p-n junction.
(a) Forward biased: A battery is connected across p-n junction diode such that, p-type is connected to positive terminal and n-type is connected to negative terminal, then it is called forward biased. The potential difference applied should be more than 0.3 V for germanium and more than 0.7 V for silicon. Then holes from p-type region and electrons from n-type region moves towards barrier and it decreases width and height of
barrier. Hence an electric current flows through circuit. When applied potential is zero, then current also equal to zero. When P.D. Increases the current is also increases but very slowly. When applied P.D. is more than potential barrier, current in creases rapidly. This voltage is called knee voltage. The forward biased voltage at which the current through diode increases rapidly is called knee voltage
b) Reversed biased : A battery is connected across p-n junction diode such that, p-type is connected to negative terminal and n-type is connected to positive terminal, then it is called reversed biased. The holes from p type region and electrons from n-type region moves away from junction and it increases width and height of barrier. Hence there is no flow of an electric current in ideal case. In actual case current is very small (inμA) . The width of potential barrier increases and diode offer very high resistance. The very small current flows through circuit is called as reverse current. If reversed bias voltage increased then the kinetic energy of electrons increases. At certain reversed bias voltage the K.E. of electrons increases enough and they knock out the electrons from semiconductor atoms\ Therefore current suddenly increase. That certain reversed bias voltage is called as breakdown voltage. At breakdown voltage the current increases suddenly and destroy the junction permanently. The reversed bas voltage at which P-N junction breaks and current suddenly increases is called as breakdown voltage.
APPEARS IN
संबंधित प्रश्न
(i) Explain with the help of a diagram the formation of depletion region and barrier potential in a pn junction.
What causes the setting up of high electric field even for small reverse bias voltage across the diode?
In the following diagram 'S' is a semiconductor. Would you increase or decrease the value of R to keep the reading of the ammeter A constant when S is heated? Give reason for your answer.
The graph shown in the figure represents a plot of current versus voltage for a given semiconductor. Identify the region, if any, over which the semiconductor has a negative resistance.
Why is a zener diode considered as a special purpose semiconductor diode?
With reference to semi-conductors answer the following :
(i) What is the change in the resistance of the semi-conductor with increase in temperature ?
(ii) Name the majority charge carriers in n-type semi-conductor.
(iii) What is meant by doping ?
The power delivered in the plate circular of a diode is 1.0 W when the plate voltage is 36 V. Find the power delivered if the plate voltage is increased to 49 V. Assume Langmuir-Child equation to hold.
The dynamic plate resistance of a triode value is 10 kΩ. Find the change in the plate current if the plate voltage is changed from 200 V to 220 V.
Answer the following question.
Why photodiodes are required to operate in reverse bias? Explain.
Basic materials used in the present solid state electronic devices like diode, transistor, ICs, etc are ______.
We use alloys for making standard resistors because they have ____________.
What are the applications of p - n Junction diode?
Of the diodes shown in the following diagrams, which one is reverse biased?
Use a transistor as an amplition
The expected energy of the electron at absolute zero is called:-
Avalanche breakdown is due to ______.
Can the potential barrier across a p-n junction be measured by simply connecting a voltmeter across the junction?
Consider a box with three terminals on top of it as shown in figure (a):
 (a) |
Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement. A student performs an experiment in which any two of these three terminals are connected in the circuit shown in figure (b).
 (b) |
The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit. The graphs are
(i) when A is positive and B is negative
 (c) |
(ii) when A is negative and B is positive
 (d) |
(iii) When B is negative and C is positive
|
(e) |
(iv) When B is positive and C is negative
 (f) |
(v) When A is positive and C is negative
 (g) |
(vi) When A is negative and C is positive
 (h) |
From these graphs of current-voltage characteristics shown in figure (c) to (h), determine the arrangement of components between A, B and C.
Read the following paragraph and answer the questions that follow.
| A semiconductor diode is basically a pn junction with metallic contacts provided at the ends for the application of an external voltage. It is a two-terminal device. When an external voltage is applied across a semiconductor diode such that the p-side is connected to the positive terminal of the battery and the n-side to the negative terminal, it is said to be forward-biased. When an external voltage is applied across the diode such that the n-side is positive and the p-side is negative, it is said to be reverse-biased. An ideal diode is one whose resistance in forward biasing is zero and the resistance is infinite in reverse biasing. When the diode is forward biased, it is found that beyond forward voltage called knee voltage, the conductivity is very high. When the biasing voltage is more than the knee voltage the potential barrier is overcome and the current increases rapidly with an increase in forward voltage. When the diode is reverse biased, the reverse bias voltage produces a very small current of about a few microamperes which almost remains constant with bias. This small current is a reverse saturation current. |
- In the given figure, a diode D is connected to an external resistance R = 100 Ω and an emf of 3.5 V. If the barrier potential developed across the diode is 0.5 V, the current in the circuit will be:
(a) 40 mA
(b) 20 mA
(c) 35 mA
(d) 30 mA - In which of the following figures, the pn diode is reverse biased?
(a)
(b)
(c)
(d)
- Based on the V-I characteristics of the diode, we can classify the diode as:
(a) bilateral device
(b) ohmic device
(c) non-ohmic device
(d) passive element
OR
Two identical PN junctions can be connected in series by three different methods as shown in the figure. If the potential difference in the junctions is the same, then the correct connections will be:
(a) in the circuits (1) and (2)
(b) in the circuits (2) and (3)
(c) in the circuits (1) and (3)
(d) only in the circuit (1) 
The V-I characteristic of a diode is shown in the figure. The ratio of the resistance of the diode at I = 15 mA to the resistance at V = -10 V is
(a) 100
(b) 106
(c) 10
(d) 10-6
With reference to a semiconductor diode, define the potential barrier.
A full wave rectifier circuit diodes (D1) and (D2) is shown in the figure. If input supply voltage Vin = 220 sin (100 πt) volt, then at t = 15 ms.
Choose the correct circuit which can achieve the bridge balance.
What occurs near the junction when the p-side and n-side are joined?
What is left behind near the junction, creating a depletion layer?
What is the approximate cut-in voltage of a germanium diode?
What is the approximate cut-in voltage of a silicon diode?
Which practical effect is associated with reverse bias before breakdown?
How does effective resistance compare between forward bias after the cut-in voltage and reverse bias before breakdown?
