P24L-2005_Incourse_Test - [6] 4. (a) Describe what is meant...

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1 DEPARTMENT OF PHYSICS P24L INCOURSE TEST TUESDAY, MARCH 8, 2005 - 11:00 a.m . TIME : 1 Hour ANSWER ALL QUESTIONS 1.(a) Why are Field Effect Transistors considered unipolar transistors? [2] (b) State the two regions within which the JFET operates. Also write down the conditions that must be satisfied for the JFET to operate in these regions. [4] (c) Use diagrams, where necessary, to describe the physical operation of a n-channel JFET with small drain-to-source voltage V DS and a varying gate-to-source voltage V GS . [8] 2. Analyze the circuit shown in Fig. 2(a) to determine the value of I D and V D . The FET has V p = - 4 V and I DSS = 10 mA . [6] R D = 10 k V DD = 15 V V D Figure 2 I D
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2 3.(a) What is a Schottky Barrier Diode? (b) Explain, with the aid of diagrams showing the energy band structure before and after contact, how the rectifying contact arises.
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Unformatted text preview: [6] 4. (a) Describe what is meant by avalanche breakdown . [2] (b) In the analysis of the Zener shunt regulator circuit, the Zener diode is considered to be source of emf in series with a dynamic resistance. Explain, with the aid of a diagram, how this is consistent with the I – V characteristic of the diode. [3] (c) The resistor R in a Zener shunt regulator circuit is chosen to be 200 Ω . The output voltage is 5.3 V when the diode current is 15 mA and the supply voltage is 10.1 V . The output voltage changes to 5.2 V whilst the diode current is 5 mA for a supply voltage of 9.8 V . Determine: (i) the output voltage when the diode current is zero (ii) the dynamic resistance r (iii) the current through R and the load current when the output voltage is 5.3 V (iv) the load regulation [9]...
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P24L-2005_Incourse_Test - [6] 4. (a) Describe what is meant...

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