Section 4–3 BJT Characteristics and Parameters

7. What is the aDC when IC 8.23 mA and IE 8.69 mA?

8. A certain transistor has an IC 25 mA and an IB 200 mA. Determine the bDC.

9. What is the bDC of a transistor if IC 20.3 mA and IE 20.5 mA?

10. What is the aDC if IC 5.35 mA and IB 50 mA?

11. A certain transistor exhibits an aDC of 0.96. Determine IC when IE 9.35 mA.===

====

==

12. A base current of 50 mA is applied to the transistor in Figure 4–53, and a voltage of 5 V isdropped across RC. Determine the bDC of the transistor.

13. Calculate aDC for the transistor in Problem 12.

14. Assume that the transistor in the circuit of Figure 4–53 is replaced with one having a bdc of200. Determine IB, IC, IE, and VCE given that VCC 10 V and VBB 3 V.

15. If VCC is increased to 15 V in Figure 4–53, how much do the currents and VCE change?

16. Determine each current in Figure 4–54. What is the bDC?

= =

–

+–

+

RC 1.0 k�

100 k�

VBB

VCC

RB

� FIGURE 4–53

17. Find VCE, VBE, and VCB in both circuits of Figure 4–55.

–

+

RC 470 �

–

+

RB

4.7 k�VBB4 V

VCC24 V

8 V–

+

� FIGURE 4–54

–

+

RC180 �

3.9 k�–

+

VBB5 V

(a)

RB

βDC = 50

VCC15 V

–

+

390 �

27 k�

–

+VBB3 V

(b)

RB

βDC = 125

VCC8 V

RC

18. Determine whether or not the transistors in Figure 4–55 are saturated.

19. Find IB, IE, and IC in Figure 4–56. aDC 0.98.=

� FIGURE 4–55

RE1.0 k�

–

+

–

+VBB2 V

VCC10 V

� FIGURE 4–56

21. If the bDC in Figure 4–57(a) changes from 100 to 150 due to a temperature increase, what isthe change in collector current?

22. A certain transistor is to be operated at a collector current of 50 mA. How high can VCE gowithout exceeding a PD(max) of 1.2 W?

23. The power dissipation derating factor for a certain transistor is 1 mW/°C. The PD(max) is 0.5 Wat 25°C. What is PD(max) at 100°C?

20. Determine the terminal voltages of each transistor with respect to ground for each circuit inFigure 4–57. Also determine VCE, VBE, and VCB.

RE10 k�

–

+

+

–VBB10 V

(a)

VCC20 V

+

–

RE2.2 k�

–

+VBB4 V

(b)

VCC12 V

� FIGURE 4–57

Section 4–4 The BJT as an Amplifier

24. A transistor amplifier has a voltage gain of 50. What is the output voltage when the input volt-age is 100 mV?

25. To achieve an output of 10 V with an input of 300 mV, what voltage gain is required?

26. A 50 mV signal is applied to the base of a properly biased transistor with 10 Æ andRC 560 Æ. Determine the signal voltage at the collector.

27. Determine the value of the collector resistor in an npn transistor amplifier with bDC 250,VBB 2.5 V, VCC 9 V, VCE 4 V, and RB 100 kÆ.

28. What is the dc current gain of each circuit in Figure 4–55?

= = = ==

=r¿ =e

Section 4–5 The BJT as a Switch

29. Determine IC(sat) for the transistor in Figure 4–58. What is the value of IB necessary to producesaturation? What minimum value of VIN is necessary for saturation? Assume VCE(sat) 0 V.=

10 k�

RB

1.0 M�

VIN β DC = 150

+5 V� FIGURE 4–58

30. The transistor in Figure 4–59 has a bDC of 50. Determine the value of RB required to ensuresaturation when VIN is 5 V. What must VIN be to cut off the transistor? Assume VCE(sat) 0 V.=

1.2 k�

RB

VIN

+15 V� FIGURE 4–59

DC in terms of bDC.

51. A certain 2N3904 dc bias circuit with the following values is in saturation. IB 500 mA,VCC 10 V, and RC 180 Æ, hFE 150. If you increase VCC to 15 V, does the transistorcome out of saturation? If so, what is the collector-to-emitter voltage and the collector current?

52. Design a dc bias circuit for a 2N3904 operating from a collector supply voltage of 9 V and abase-bias voltage of 3 V that will supply 150 mA to a resistive load that acts as the collectorresistor. The circuit must not be in saturation. Assume the minimum specified bDC from thedatasheet.

53. Modify the design in Problem 52 to use a single 9 V dc source rather than two differentsources. Other requirements remain the same.

54. Design a dc bias circuit for an amplifier in which the voltage gain is to be a minimum of 50 andthe output signal voltage is to be “riding” on a dc level of 5 V. The maximum input signal volt-age at the base is 10 mV rms. VCC 12 V, and VBB 4 V. Assume 8 Æ.r¿ =e= =

= = ==

50. Derive a formula for a