Problem 61-2    Source:  Problem elaborated by the author of the site.

Suppose a diode having a potential difference of 0.6 volt when it circulates through it current of 1 mA. In addition, assume that the voltage drop on the diode varies from 0.1 volt for every decade of variation in the electric current. Based on this information determine the current and voltage on the diode in the circuit shown in the Figure 61-02.1.

Solution of the Problem 61-2   

From the statement of the problem, it is known that the 2.3 η V_T of eq. 61-4, which was called K, is K = 0,1. It repeats itself here eq. 61-04 developed in item Diode in Conduction Zone.

On the other hand, analyzing the circuit we can write the equation that determines the current in the diode, or:

Since there are two unknowns and two related equations, we can determine the unknowns using an iteration process. The values given in the problem assume that I_D = I₁ = 1 mA and V_D = V₁ = 0.6 volt. Using these values in the above equation, we can determine a value for I₂, remembering that V_i = 9 volts. Then:

Working algebraically with eq. 61-04:

Substituting for the numerical values found so far, we obtain:

This value of V₂ is the new value of V_D. Since the previous value and this value are very different, it is necessary to perform one more iteration and compare the new values found. In this new iteration will be found V₃ and I₃, using as reference the previous values, that is, V₂ and I₂. Then:

And to V₃:

Performing the calculation:

Now see that the difference between V₃ and V₂ is of ΔV = 0.00064 volt. Note that this difference is insignificant. Then, we can say that the values of voltage and current in the diode are: