Analog Electronics

Temperature effect on diode

The following graph shows the effect of temperature on the characteristics of diode

A-B curve: This curve shows the characteristics of diode for different temperatures in the forward biase. As we can see from the figure given above, that curve moves towards left as we increase the temperature. We know with increase in temperature, conductivity of semiconductors increase. The intrinsic concentration (ni) of the semiconductors is dependent on temperature as given by:

                                         Eg is the energy gap

K is a voltage man constant

A is a constant independent of temperature

When temperature is high, the electrons of the outermost shell take the thermal energy and become free. So conductivity increases with temperature. Hence with increase in temperature, the A-B curve would shift towards left i.e. curve would rise sharply and the breakdown voltage would also decrease with increase in temperature.

A-C curve: This curve shows the characteristics of diode in the reverse biased region till the breakdown voltage for different temperatures. We know ni concentration would increase with increase in temperature and hence minority charges would increase with increase in temperature. The minority charge carriers are also known as thermally generated carriers and the reverse current depends on minority carriers only. Hence as the number of minority charge carriers increase, the reverse current would also increase with temperature as shown in the figure given on the previous page.      

                The reverse saturation current gets double with every 10 C increase in temperature.

C-D curve: This curve shows the characteristics of a diode in reverse biased region from the breakdown voltage point onwards. As with increase in temperature, loosely bonded electrons are already free and to free the other electrons, it would take more voltage than earlier. Hence breakdown voltage increases with increase in temperature as depicted in the figure shown in the figure given on the previous page..

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