Download sem i 2008/09 lecture ii : bjt current relationship & dc analysis

DMT 231/3 Electronic II
Lecture II
BJT
Current Relationship & DC Analysis
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT CURRENT RELATIONSHIPS
1. Given that a common-emitter current gain β = 150 and a base current iB =
15 µA.
Assume that the transistor is biased in the forward-active mode.
Determine:
(i)
collector current iC ,
(ii) emitter current iE and
(iii) common-base current gain α.
2. Transistors of a particular type have common-base current gains in the
range of 0.980 ≤ α ≤ 0.995.
Determine the corresponding range of common-emitter current gain β.
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT CURRENT RELATIONSHIPS
3. The common-emitter current gains of two transistors are β1 = 75 and β2 =
125.
Determine the common-base current gains, α1 and α2 .
4. An npn transistor is biased in the forward-active mode.
The base current is iB = 9.60 µA and emitter current, iE = 0.780 mA.
Determine:
(i)
common-emitter current gain β,
(ii) common-base current gain α, and
(iii) collector current iC.
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT CURRENT RELATIONSHIPS
5. The emitter current in a pnp transistor biased in the forward-active mode
is iE = 2.15 mA. The common-base current gain α = 0.990.
Determine:
(i)
common-emitter current gain β,
(ii) base current iB , and
(iii) collector current iC.
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT COMMON-EMITTER
AMPLIFIER – DC ANALYSIS
VBE(ON) = 0.7 V
β = 200
1. Determine:
(i)
(ii)
(iii)
(iv)
base current IB ,
emitter current IE ,
collector current IC
collector-emitter voltage,
VCE and
Figure 1
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT COMMON-EMITTER
AMPLIFIER – DC ANALYSIS
2. The circuit elements in Figure 1 are changed to VCC = 5 V, VBB = 2 V,
RC = 4 kΩ, and RB = 200 kΩ
Determine:
(i)
(ii)
(iii)
(iv)
SEM I 2008/09
base current IB ,
emitter current IE ,
collector current IC and
collector-emitter voltage, VCE
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS
BJT AS AMPLIFLYING DEVICE
1.
Explain the purpose of a thin, lightly doped base region.
2. To operate as an amplifier, the base-emitter is
__________-biased and the base-collector is
____________-biased.
SEM I 2008/09
LECTURE II : BJT CURRENT RELATIONSHIP & DC ANALYSIS