Question 1 A diode circuit diagram is shown in Figure 1.  Assuming that the diode voltage drop is         0.7 V, calculate the value of the resistor R such that the diode current is 0.25 mA.  All the resistor values are in ohms.

Figure 1 (The resistor values are in ohms)

Question 2

Figure 2 shows a + 5 V power supply built using a transformer, bridge rectifier, capacitor filter and 7805 regulator. The power supply has to deliver a current of 200 mA.  The maximum and minimum input required for 7805 regulator for proper operation are +20 V and + 7.3 V, respectively.   Verify whether the 7805 and hence the power supply can function properly or not.   If the 7805 is working properly and has a ripple rejection ratio of 70 dB, what is the ripple voltage at the output of 7805?

Figure 2 (The capacitor values are in F)

Question 3

A transistor biasing circuit is shown in Figure 3.  Given that  of the transistor is 100 and  VCE (SAT) of the transistor is 0.3 V, identify whether the transistor is in the linear region or saturation region.  Justify your answer by giving appropriate reasons

Figure 3 (The resistor values are in ohms)

Question 4                                                                                                                         

The schematic of a common emitter amplifier is shown in Figure 4.  The transistor has a  value of 200.

(a) Find the DC operating point of the transistor.                                                   

(b) Calculate the AC emitter resistance re’.                                                               

(c) Calculate the voltage gain of the amplifier.                                                      

(d) Calculate the base and stage input impedances.                                            

(e) Calculate the low cut-off frequency for the collector coupling circuit.           

(f) Calculate the low cut-off frequency for emitter bypass circuit.                      

Figure 4 (The resistor values are in ohms and capacitor values are in F)

Question 5

The schematic of an OPAMP circuit is shown in Figure 5.  Show that the output voltage is

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