254
♦
TRANSISTOR BIAS CIRCUITS
ADVANCED PROBLEMS
49. Design a circuit using base bias that operates from a 15 V de voltage and draws a maximum
current from the de source (lcqmax)) of 10 mA. The Q-point values are to be le = 5 mA and
VCE = 5 V. The transistor is a 2N3904. Assume a midpoint value for /Joe.
50. Design a circuit using emitter bias that operates from de voltages of+ 12 V and -12 V. The
maximum Ice is to be 20 mA and the Q-point is at 10 mA and 4 V. The transistor is a 2N3904.
51. Design a circuit using voltage-divider bias for the following specifications: Vee = 9 V,
Icqmax) = 5 mA, le = 1.5 mA, and VCE = 3 V. The transistor is a 2N3904.
52. Design a collector-feedback circuit using a 2N2222A with Vee = 5V, le = 10 mA, and
VCE = 1.5V.
53. Can you replace the 2N3904 in Figure 5--47 with a 2N2222A and maintain the same range of
output voltage over a temperature range from 45°C to 55°C?
54. Refer to the datasheet graph in Figure 5-50 and the partial datasheet in Figure 5--49. Determine
the minimum de current gain for a 2N2222A at -55°C, 25°C, and 175°C for VCE = 1 V.
Ci
·c1
4.0
3.0
i:i 2.0
.g
- _,_ ...
0.7
Ci
J 0.3
� ,_ ,_
-
...
1.0
0.5
T1 = 175° C
f-
0.2
0.5
_,_ ...
-
-
25° C
,_ i-- 1,_
I
... - - -- - - - -
---- -� �- -- ....
... - - -- - - - - - -...
�- -
-·- ...
55° c
-- -
- -
I
I
I
I
Vrn = 1.0V- - - Vrn = lOV-
�
r-....
i::. .....
'-
�
"'-
r-'
�
" - -- -..
'0
'" '
�
,�
-� "�
-
'I:
'\
\
'\:
0.7
1.0
2.0
3.0
5.0
10
20
30
50
70
100
I'300
200
500
le, collector current (mA)
_. FIGURE 5-50
55. A design change is required in the valve interface circuit of the temperature-control system
shown in Figure 5-28. The new design will have a valve interface input resistance of 10 kll.
Determine the effect this change has on the temperature-to-voltage conversion circuit.
56. Investigate the feasibility of redesigning the temperature-to-voltage conversion circuit in Figure
5-29 to operate from a de supply voltage of 5.1 V and produce the same range of output volt­
ages determined in the Device Application over the required thermistor temperature range from
60°C to 80°C.
MULTISIM TROUBLESHOOTING PROBLEMS
These file circuits are in the Troubleshooting Problems folder on the website.
57. Open file TPM05-57 and determine the fault.
58. Open file TPM05-58 and determine the fault.
59. Open file TPM05-59 and determine the fault.
60. Open file TPM05-60 and determine the fault.
61. Open file TPM05-61 and determine the fault.
62. Open file TPM05-62 and determine the fault.