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Question : 26
Total: 37
(a) Why is a photodiode operated under reverse bias condition?
(b) Draw V-I characteristic curves of photodiode for incident light of intensitiesI 1 I 2 ( I 1 > I 2 )
OR
(a) State the level of doping and biasing condition used in light emitting diode (LED).
(b) Write any two advantages of LED over the conventional low power lamps.
(b) Draw V-I characteristic curves of photodiode for incident light of intensities
OR
(a) State the level of doping and biasing condition used in light emitting diode (LED).
(b) Write any two advantages of LED over the conventional low power lamps.
Solution:
(a) Photodiodes conduct in reverse biased condition only when a light of suitable frequency is incident on it. During reverse bias, the current is mainly due to the drift of minority charge carriers crossing the junction. The variation in intensity of light affects the minority charge carriers concentration and hence the reverse current is predominant.
In forward bias condition, the change in majority charge carriers is not much affected by light intensity and hence the forward current variation is not so predominant.
Hence, photodiodes are operated in reverse bias condition.
(b)
OR
(a) LED is normally a heavily dopedp − n
LED is always operated in forward bias condition.
(b) LED has longer life span as compared to conventional lamps.
LED is extremely energy efficient device and may consume up to90 %
In forward bias condition, the change in majority charge carriers is not much affected by light intensity and hence the forward current variation is not so predominant.
Hence, photodiodes are operated in reverse bias condition.
(b)
OR
(a) LED is normally a heavily doped
LED is always operated in forward bias condition.
(b) LED has longer life span as compared to conventional lamps.
LED is extremely energy efficient device and may consume up to
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