EMK11303 – ELECTRONICS 1
Tutorial 4 (Bipolar Junction Transistor – BJT)
1. Why is the base current in a transistor so much less than the collector current?
2. Figure 4.1 shows a base current of 50µA is applied to transistor and a voltage drop of
4V is dropped across RC. Determine:
(a) αDC
(b) βDC
2kΩ
100kΩ
Figure 4.1
3. Assume that the transistor in Figure 4.1 is replaced with one a having a βDC of 150.
Given that VCC = 10V and VBB 2.5V. Determine:
(a) IB
(b) IC
(c) IE
4. The BJT circuit in Figure 4.2 has hFE = 200, determine
(a) base current
(b) base resistance
Figure 4.2
5. For both circuits in Figure 4.3, determine:
(a) VCE
Prepared by : Dr Liew Hui Fang
Page 1
EMK11303 – ELECTRONICS 1
(b) VBE
(c) VCB
(d) whether or not the transistors are saturated?
RC
200 Ω
RB
4 kΩ
VCC
15V
RB
30 kΩ
βDC
VBB
5V
RC
400 Ω
βDC
VBB
4V
50
Figure 4.3 (a)
VCC
10V
150
Figure 4.4 (b)
6. Based on Figure 4.4, determine the terminal voltages of transistor with respect to the
ground and also determine VCE, VBE and VCB.
VCC
10V
VBB
5V
RE
5 kΩ
Figure 4.4
7. A 50mV signal is applied to the base of a properly biased transistor with r’e = 10 Ω
and Rc = 600 Ω. Determine the signal voltage at collector.
8. Determine the value of collector resistor in an npn transistor amplifier with βDC = 250,
VBB = 2.5V, VCC = 9V, VCE = 4V and RB = 100 kΩ.
Prepared by : Dr Liew Hui Fang
Page 2
EMK11303 – ELECTRONICS 1
9. Based on Figure 4.5, assume VCE(sat) = 0. Determine:
(a) value of IC(sat)
(b) value of IB necessary to produce saturation?
(c) minimum value of VIN is necessary for saturation?
5V
10kΩ
βDC
150
1 MΩ
Figure 4.5
10. Based on Figure 4.6, assume VCE(sat) = 0. Determine:
(a) value of RB required to ensure saturation when VIN = 5V
(b) what must VIN be to cut off the transistor?
5V
1.2 kΩ
βDC
50
Figure 4.6
Prepared by : Dr Liew Hui Fang
Page 3