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Explain the effect of temperature on PN junction diode.
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• PN junction diode parameters like reverse saturation current, bias current, reverse breakdown voltage and barrier voltage are dependent on temperature.
• Mathematically diode current is given by

$I = IS * (exp(^{(V/(n*k*T/q))}) –1)$

Hence from equation we conclude that the current should decrease with increase in temperature but exactly opposite occurs there are two reasons:

• Rise in temperature generates more electron-hole pair thus conductivity increases and thus increase in current
• Increase in reverse saturation current with temperature offsets the effect of rise in temperature
• Reverse saturation current $(I_S)$ of diode increases with increase in the temperature the rise is 7%/ºC for both germanium and silicon and approximately doubles for every $10ºC$ rise in temperature.
• Thus if we kept the voltage constant, as we increase temperature the current increases.
• Barrier voltage is also dependent on temperature it decreases by 2mV/ºC for germanium and silicon.
• Reverse breakdown voltage $(V_R)$ also increases as we increase the temperature.

Fig1 Characteristics of diode with respect to temperature

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