Download Lecture_10_BJT

Survey
yes no Was this document useful for you?
   Thank you for your participation!

* Your assessment is very important for improving the work of artificial intelligence, which forms the content of this project

Document related concepts

Signal-flow graph wikipedia, lookup

Tube sound wikipedia, lookup

Voltage optimisation wikipedia, lookup

Thermal runaway wikipedia, lookup

Stray voltage wikipedia, lookup

Mains electricity wikipedia, lookup

Ohm's law wikipedia, lookup

Rectifier wikipedia, lookup

Islanding wikipedia, lookup

Surge protector wikipedia, lookup

Power electronics wikipedia, lookup

Voltage regulator wikipedia, lookup

Schmitt trigger wikipedia, lookup

Resistive opto-isolator wikipedia, lookup

Alternating current wikipedia, lookup

Switched-mode power supply wikipedia, lookup

TRIAC wikipedia, lookup

Current source wikipedia, lookup

Semiconductor device wikipedia, lookup

Regenerative circuit wikipedia, lookup

P–n diode wikipedia, lookup

Buck converter wikipedia, lookup

Metadyne wikipedia, lookup

History of the transistor wikipedia, lookup

Two-port network wikipedia, lookup

Opto-isolator wikipedia, lookup

Network analysis (electrical circuits) wikipedia, lookup

Transistor wikipedia, lookup

Current mirror wikipedia, lookup

Transcript
Lecture 10
Bipolar Junction Transistor
(BJT)
BJT
1-1
Outline
 Continue BJT
 Continue DC analysis
• More examples

Introduction to AC signal analysis
BJT
1-2
Example (1)
 A bipolar transistor having IS = 5×10-16 A is
biased in the forward active region with VBE
=750 mV. If the current gain (or β) varies from
50 to 200 due to manufacturing variations,
calculate the minimum and maximum terminal
currents of the device.
BJT
1-3
Solution
 For a given VBE, the collector current remains
independent of β
 The base current varies from IC/200 to IC/50:
 the emitter current experiences only a small
variation because (β+ 1)/β is near unity for large
β:
BJT
1-4
Example (2)
 Determine the dc level of IB and VC for the
BJT circuit
BJT
1-5
Solution
 For the dc mode,
the capacitor assumes
the open-circuit equivalence
and RB =R1+R2
BJT
1-6
Example (3)
 Determine the dc bias voltage VCE and the current
IC for the voltage-divider configuration shown in
the figure. (use exact and approximate methods)
BJT
1-7
Solution
 Using Exact Analysis Method
BJT
1-8
Solution (cont’d)
 Return to the example:
BJT
1-9
Solution (cont’d)
BJT
1-10
Solution (cont’d)
 Using Approximate Analysis Method
The condition that will define
whether the approximate approach
can be applied
BJT
1-11
Solution (cont’d)
 Return to the example:

Testing:
BJT
1-12
Solution (cont’d)
Now, compare between obtained results by the exact
and approximate methods
BJT
1-13
Example (4)
 Determine the voltage VCB and the current IB
for the common-base configuration as shown in
figure
BJT
1-14
Solution
 Applying Kirchhoff’s voltage law to the input
circuit yields
 Applying Kirchhoff’s voltage law to the output
circuit gives
BJT
1-15
Example (5)
 Given the device characteristics as shown
in figure, determine VCC, RB, and RC for the
fixed bias configuration
BJT
1-16
Solution
 From the load line
BJT
1-17
BJT Transistor Modeling
 A model is an equivalent circuit that represents
the AC characteristics of the transistor
 A model uses circuit elements that
approximate the behavior of the transistor
 There are two models commonly used in small
signal AC analysis of a transistor:
 re
model
 Hybrid equivalent model
BJT
1-18
BJT AC Analysis
BJT
1-19
The re Transistor Model
 BJTs are basically current-controlled devices;
therefore the re model uses a diode and a
current source to duplicate the behavior of the
transistor

Recall (from lecture 5): the ac resistance of a diode
can be determined by the equation r = 26 mV/ID,
where ID is the dc current through the diode at the
Q (quiescent) point
ac
 One disadvantage to this model is its sensitivity
to the DC level. This model is designed for
specific circuit conditions
BJT
1-20
Common-Base Configuration
I c  I e
re 
26 mV
Ie
Input impedance:
Zi  re
Output impedance:
Zo  
Voltage gain:
AV 
Forwardbiased
junction
I e R L R L

I e re
re
Current gain:
RL
Ai    1
BJT
1-21
Example
 For a common-base configuration, as shown in
figure, with IE = 4 mA, α = 0.98, and an ac signal
of 2 mV applied between the base and emitter
terminals:
(a) Determine the input impedance.
 (b) Calculate the voltage gain if a load of 0.56 kΩ is
connected to the output terminals.
 (c) Find the output impedance and current gain.

BJT
1-22
Solution
BJT
1-23
Lecture Summary
Covered material
 Continue BJT

DC analysis
• More examples

Introduction to AC signal analysis
Material to be covered next lecture
 Continue BJT analysis with AC signal
BJT
1-24