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प्रश्न
Answer the following question.
Why photodiodes are required to operate in reverse bias? Explain.
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उत्तर
The photodiode is reverse biased for operating in the photoconductive mode. As the photodiode is in reverse bias, the width of the depletion layer increases. This reduces the junction capacitance and thereby the response time. In effect, the reverse bias causes faster response times for the photodiode. The photocurrent is linearly proportional to the illuminance.
संबंधित प्रश्न
(i) Explain with the help of a diagram the formation of depletion region and barrier potential in a pn junction.
Explain the working of P-N junction diode in forward and reverse biased mode.
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.
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 ?
In forward bias width of potential barrier in a p + n junction diode
When an electric field is applied across a semiconductor ______.
- electrons move from lower energy level to higher energy level in the conduction band.
- electrons move from higher energy level to lower energy level in the conduction band.
- holes in the valence band move from higher energy level to lower energy level.
- holes in the valence band move from lower energy level to higher energy level.
If each diode in figure has a forward bias resistance of 25 Ω and infinite resistance in reverse bias, what will be the values of the current I1, I2, I3 and I4?
Answer the following giving reasons:
A p-n junction diode is damaged by a strong current.
Describe the following term briefly:
breakdown voltage in reverse biasing
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
