) . That is, r V F F F = ∆ ∆ (iv) Thus the diode behaves as a conductor when it is forward biased. However, if the applied voltage is increased beyond a rated value, it will produce an extremely large current which may destroy the junction due to overheating. This is called as the breakdown of the diode and the voltage at which the diode breaks down is called the breakdown voltage.
Thus, it is safe to operate a diode between the threshold voltage and the breakdown voltage. ii) Reverse characteristics The circuit to study the reverse characteristics is shown in Figure . (a). In the reverse bias, the p -side of the diode is connected to the negative terminal and n -side to the positive terminal of the dc power supply.
A graph drawn between the reverse bias voltage and the current across the junction is called the reverse characteristics of a p-n junction diode. It is shown in Figure . (b). Under this bias, a very small µA ( –15V) – – – V R (a) D Reverse bias Reverse breakdown voltage (b) I F (mA) – I R ( µ A) – V R (V) Figure .
p-n junction diode (a) Diode under reverse bias (b) Reverse characteristics current in µA flows across the junction. This is due to the flow of the minority charge carriers and is called t he leakage current or reverse saturation current. This reverse current is independent of the voltage up to a certain voltage, known as breakdown voltage. Ideal diode: It acts like a conductor when it is forward biased.
When it is reverse biased, it acts like an insulator. For ideal diodes, the forward resistance is zero and barrier potential is considered negligible. Note The forward and reverse charactristics are given in one graph as shown in Figure . .
- - - - - - - - Unit electronics and Communication EXAMPLE . A silicon diode is connected with 1kΩ resistor as shown. Find the value of current flowing through AB . 1kΩ – .