Q39 of 40 Page 93

For the transistor circuit shown in Fig.14.19, evaluate VE, RB, RE given IC = 1 mA, VCE = 3V, VBE = 0.5 V and VCC = 12 V, β = 100.


Circuit Diagram:



From loop1 we get,



Also,






Now VE is the potential drop across RE. Hence,




To find RB we need to find the current through it. This can be done by finding the potential across the 20k resistance.




Also 0.01mA current goes to the base. Hence amount of current through RB will be iB=0.0945mA.


So, the value of RB will be,





More from this chapter

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36

Suppose a ‘n’-type wafer is created by doping Si crystal having 5 × 1028 atoms/m3 with 1ppm concentration of As. On the surface 200 ppm Boron is added to create ‘P’ region in this wafer. Considering ni = 1.5 × 1016 m–3, (i) Calculate the densities of the charge carriers in the n & p regions. (ii) Comment which charge carriers would contribute largely for the reverse saturation current when diode is reverse biased.

 37

An X-OR gate has following truth table:

It is represented by following logic relation



Build this gate using AND, OR and NOT gates.


 38

Consider a box with three terminals on top of it as shown in Fig.14.18 (a):


Three components namely, two germanium diodes and one resistor are connected across these three terminals in some arrangement.


A student performs an experiment in which any two of these three terminals are connected in the circuit shown in Fig. 14.18 (b).



The student obtains graphs of current-voltage characteristics for unknown combination of components between the two terminals connected in the circuit.


The graphs are


(i) when A is positive and B is negative



(ii) when A is negative and B is positive



(iii) When B is negative and C is positive



(iv) When B is positive and C is negative



(v) When A is positive and C is negative



(vi) When A is negative and C is positive



From these graphs of current – voltage characteristic shown in Fig. 14.18 (c) to (h), determine the arrangement of components between A, B and C.


 40

In the circuit shown in Fig.14.20, find the value of RC.