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Explain briefly, with the help of circuit diagram , how V-I characteristics of a p-n junction diode are obtained in (i) forward bias, and (ii) reverse bias. Draw the shapes of the characteristic curves obtained. Or Explain briefly, with the help of necessary diagrams, the forward and the reverse biasing of a p-n junction diode. Also draw their characteristic curves in the two cases. |
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Answer» Solution :WORKING of a p-n JUNCTION diode can be studied in (i) FORWARD bias, and (ii) reverse bias arrangement. To study characteristics of a p-n junction in these biasing arrangement we proceed as follows (i) Forward bias : In forward bias arrangementp-side of p-n junction is connected to +ve terminal of battery and n-side to -ve terminal of battery as shown in . A voltmeter V and a milliammeter mA are joined as shown in figure. The voltage applied to p-n junction can be altered by using a rheostat with battery. In forward bias, the current `I_(e)` first increases very slowly till a certain threshold voltag ( ~ 0.7 V for silicon diode) is reached. After the threshold voltage, the diode current increases exponentially even for a very small increase in the diode bias voltage. The characteristic curve is shown in. (ii) Reverse bias: In reverse bias arrangementp-side of p-n junction is connected to -ve terminal and n-side to +ve terminal of battery as shown in . A voltmeter V and a microammeter uA (since current in reverse bias is extremely small) are also connected as shown. In reverse bias the battery is capable of providing a voltage of even up to 100 V. Inreverse bias, the current `I_(R)` is very small and ALMOST remains constant with change in reverse bias voltage `V_(R)`. It is called "reverse saturation current". However, at very high reverse bias the current suddenly increases. This voltage is known as the breakdown voltage or zener voltage. The characteristic curve is shown in .  
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