Finding the region of operation of transistor is discussed

1. UNIT-III
Bipolar Junction Transistor Biasing
& Amplifiers at low frequencies
ANIL NEERUKONDA INSTITUTE OF TECHNOLOGY & SCIENCES(A)
Department of Electronics and Communication Engineering

2. Region of Operation
Sem-I/ECA-I/ANIL PRASAD D 2
Region of
operation
Cut-off
JE:RB
JC:RB
VBE<0.5V
IB=0A
VBC<0.4
VCB>-0.4
IC=0A
VEB<0.5V
IB=0A
VCB<0.4
IC=0A

3. Region of operation
Region of
operation
Active
JE:FB
JC:RB
VBE=0.7V
IB>0A
VBC<0.4
VCB>-0.4
IC=βIB
VBE=0.7V
IB>0A
VCB<0.4
IC=βIB

4. Region of operation
Region of
operation
Saturation
JE:FB
JC:FB
VBE=0.7V
IB>0A
VBC>0.5
VCB<-0.5
VCE=0.2
VBE=0.7V
IB>0A
VCB>0.5
VCE=-0.2
VEC=0.2

5. Region of operation
• Method-I
1. Assume transistor is in Active region
2. Determine voltages and currents
3. Determine VCB (check for consistency of results)
If VCB is positive for npn JC is RB
If VCB is negative for npn JC is FB
If VCB is positive for pnp JC is FB
If VCB is negative for pnp JC is RB
IC=βIB IC=αIE

6. Region of operation
• Method-II
1. Assume transistor is in Saturation region
are not valid
2. Determine voltages and currents using |VBE|=0.7 and
|VCE|=0.2V
3. Determine
4. Check for consistency of results
IC=βIB IC=αIE
β
(sat)I
I C
MinB, 
)saturationinisr(TransistoII MinB,B 
Active)inisr(TransistoII MinB,B 

7. Problems
• #1. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+4V.
Sol:
Step1:Assume Transistor is in Active region
Step2: Assume VBE=0.7V
VBE=VB-VE
VE=VB-VBE=4-0.7=3.3V
4V
10V+4V
+10V
0.7
mA1
3.3K
3.3V
R
V
I
E
E
E 

 VE

8. Problems
• #1. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+4V.
Sol:
Step3:
Step4: VC=VCC-ICRC
=10-0.99×4.7
=5.3V
4V
10V+4V
+10V
0.7
VE
IC=αIE
IC=0.99mA

9. Problems• #1. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+4V.
Sol:
Step5: Check for consistency of results
VB=4V
VCB=VC-VB
=5.3-4
=1.3V
JC is RB
BJT is in Active region
Assumption is correct 4V
10V
+10V
0.7
VE
1.3V

10. Problems
• #2. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+6V.
Sol:
Step1:Assume Transistor is in Active region
Step2: Assume VBE=0.7V
VBE=VB-VE
VE=VB-VBE=6-0.7=5.3V
6V
10V+6V
+10V
0.7
VE
IE=1.6mA

11. Problems
• #2. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+6V.
Sol:
Step3:
Step4: VC=VCC-ICRC
=10-1.568×4.7
=2.62V
6V
10V+6V
+10V
0.7
VE
IC=αIE
IC=1.568mA

12. Problems• #2. Determine all node voltages and branch currents
Given VCC=+10V,RC=4.7KΩ,RE=3.3KΩ,VB=+6V.
Sol:
Step5: Check for consistency of results
VB=6V
VCB=VC-VB
=2.62-6
= -3.74V
JC is FB
BJT is NOT in Active region
Assumption is not correct 6V
10V
+10V
0.7
VE
3.74V

13. Problem #2
• Assume that a Si transistor with β=100 and VBE=0.7V is used in the
circuit shown below. Determine the collector current IC(in mA).
A) 5mA B) 3.92mA C) 5μA D)3.92μA

14. Problem #2 solution
• Assume that a Si transistor with β=100 and VBE=0.7V is used in the
circuit shown below. Determine the collector current IC(in mA).
A) 5mA B) 3.92mA C) 5μA D)3.92μA
• IB=(2-0.7)/40 mA
• IC= βIB=5mA
• VC=10-2.5x5=10-12.5=-2.5
• VB=VBE=0.7
• VCB=-ve JC is FB
• IC=(10-0.2)/2.5 mA =3.92mA

15. Problem #3
Assume that a Si transistor with β=∞, VBE=0.7V, R1=60KΩ,
RE=500Ω and VCC=3V is used in voltage divider bias circuit shown
below. Determine the required value of R2(in KΩ) to produce
IC=1mA.
VB

16. Problem #3 Solution
Given β=∞
IC=IE ( since IB=0)
VB
12
2
RR
R
VV CCB


EBEB VVV 
EEE RIV 

17. Problem #4
• Assume that a Si transistor with β=∞ is used in voltage divider bias
circuit shown below. The Q-point is (5V,2mA). Determine the
required value of RE(in KΩ).Given RC=1.5KΩ R1=10KΩ, R2=6KΩ
and VCC=10V

18. Problem #4 solution
• Assume that a Si transistor with β=∞ is used in voltage divider bias
circuit shown below. The Q-point is (5V,2mA). Determine the
required value of RE(in KΩ).Given RC=1.5KΩ R1=10KΩ, R2=6KΩ
and VCC=10V
Given β=∞
IC=IE ( since IB=0)
Apply KVL around CE loop
EECECCCC RIVRIV 

19. Problem #5
• If the transistor in figure has high value of beta and
VBE=0.65 the current I flowing through 2KΩ is _______
Sem-I/ECA-I/ANIL PRASAD D 19

20. Thank you
for listening
Sem-I/ECA-I/ANIL PRASAD D 20