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Temperature effects

Temperature effects

From the diode equation , the thermal voltage and the reverse saturation current are temperature dependent.

The thermal voltage is directly proportional to temperature.

The reverse saturation current IS increases approximately 7.2% /°C for both silicon and germanium diodes.

The expression for the reverse saturation current as a function of temperature is

where

  • kS = 0.072 / °C.
  • T1 and T2 are two different temperatures.

Since e 0.72 is approximately equal to 2, Equation above can be simplified and rewritten as

 Example

The saturation current of a diode at 25 °C is 10-¹² A. Assuming that the emission constant of the diode is 1.9, (a) Plot the i-v characteristic of the diode at the following temperatures: T1 = 0 °C, T2 = 100 °C.

% Temperature effects on diode characteristics

% Boltzmann’s constant = 1.38e-23 J / oK
k = 1.38e-23;

% Electronic charge = 1.6e-19 Coulombs
q = 1.6e-19;

% Specifying two Temperatures
t1 = 273 + 0;
t2 = 273 + 100;

% Reverse saturation current or leakage current,
ls1 = 1.0e-12;
ks = 0.072;
ls2 = ls1*exp(ks*(t2-t1));

v = 0.45:0.01:0.7;
l1 = ls1*exp(q*v/(k*t1));
l2 = ls2*exp(q*v/(k*t2));

%Plot Diode I-V Curve at two Temperatures
plot(v,l1,'+')
hold on;
plot(v,l2,'o')

axis([0.45,0.75,0,10])
xlabel('Voltage (V)')
ylabel('Current (A)')