COMPUTING

Chapter 2 Introduction to Semiconductor Electronics − Diodes2.19 Exercises1. Plot the i– v characteristics of a forward−biased junction diode with n = 2 at 27 °C .2. Show that for a decade (factor 10) change in current i D of a forward−biased junction diodethe voltage v D changes by a factor of 2.3nV T . Hint: Start with the approximate relationi D I r e v D ⁄ nV≈T, form the ratio V D2 ⁄ V D1 corresponding to the ratio I D2 ⁄ I D1 , and plot in semilogscale.3. Suggest an experiment that will enable one to compute the numerical value of n .4. It is known that for a certain diode I r = 10 – 13 A at 50 °C. and the reverse current I rincreases by about 15% per 1 °C rise. At what temperature will I rdouble in value? Whatconclusion can we draw from the result?5. When a junction diode operates at the reverse−bias region v < 0 and before avalanche occurs,the current I ris almost constant. Assuming that v » V T we can show that i D ≈ – I rand forthis reason is often referred to as the saturation current and whereas in the forward−biasedI rregion I rhas a typical value of 10 – 14 A to 10 – 15 A at 27 °C , a typical value in the reverse−biased region is 10 – 9 A. Also, the reverse current doubles for every 10 °C rise in temperature.In the circuit below, the applied voltage V S is not sufficient to drive the diode into the avalancheregion, and it is known that = 0.5 V at 20 °C .V RV S500I KΩ rV RFind:a. V R at 0 °Cb. V R at 40 °C6. For the circuit below, find the value of V out assuming that all three diodes are ideal. Compareyour answer with that of Example 2.4. Make any reasonable assumptions.2−56Electronic Devices and Amplifier Circuits with MATLAB Computing, Second EditionCopyright © Orchard Publications