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BJT Bias Circuits: A Comprehensive Guide for Electronics Students - Prof. Ernest Kim, Lecture notes of Electronics

A detailed explanation of bjt bias circuits, covering various configurations and their stability factors. It includes diagrams, equations, and explanations for each configuration, making it a valuable resource for students studying electronics. The document also discusses the importance of bias stability and provides practical insights into circuit design.

Typology: Lecture notes

2023/2024

Uploaded on 11/22/2024

ernie-kim
ernie-kim 🇺🇸

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ELEC 301 BJT Bias Circuits 1
B
C
EE
B
C
IB
I
IE
C
IE
IC
IB
npn pnp
BJT Bias Configurations
BJT Current Relationships:
()
C
F
F
EBFEE
F
F
CBFC
F
E
B
F
C
BIIIIIIII
I
I
I
I
β
β
β
β
β
β
β
β
1
,1,
1
,,
1
,
+
=+=
+
==
+
==
BJT Bias Configuration Base-Emitter Loop Collector-Emitter Loop
Fixed Bias npn
RBRC
IBIC
+
-
VCE
+VCC
VBE -
+
RBRC
IBIC
+
-
VCE
+VCC
VBE -
+
Vγ
βFIB
(a) (b)
B
BECC
BR
VV
I
=
VVI
R
CE CC C C
=
C
B
BECC
FCCCE R
R
VV
VV
=
β
Fixed Bias w/ Emitter Feedback npn
RBRC
IBIC
+
-
VCE
+VCC
VBE -
+
IEE=-I E
RE
EEEBEBBCC RIVRIV +
+
=
E
F
F
F
B
BECC
C
R
R
VV
I
+
+
=
β
β
β
1
pf3
pf4
pf5

Partial preview of the text

Download BJT Bias Circuits: A Comprehensive Guide for Electronics Students - Prof. Ernest Kim and more Lecture notes Electronics in PDF only on Docsity!

ELEC 301

BJT Bias Circuits

1

B

C E^

E B

C

IB

IC IE

IC IE IB npn^

pnp

BJT Bias Configurations

BJT Current Relationships:

(^

)^

C F F E B F E E F F C BF C E F B C F B^

I I I I I I I I I I I I

β^ β

,^

BJT Bias Configuration

Base-Emitter Loop

Collector-Emitter Loop

Fixed Bias npnR^ B^

I^ B^ R^ C

+VCC I^ C + VCE- V^ BE^ +-

R^ B^

I^ B^ R^ C

I^ C

  • VCE - +VCC V^ BE^

V + γ

βI^ F^

B

(a)^

(b)

BE B CC B^

V R

V

I^

=^

V^

V^

I^ R

CE^

CC^

C^

C

=^

C BE B CC F CC CE^

R

V R

V

V

V^

⎛^ ⎜⎜⎝

β

Fixed Bias w/ Emitter Feedback npnR^ B^

I^ B^ R^ C

I^ C + VCE- +VCC V^ BE^ +-

= -II EE E

R^ E

E EE BE BB CC^

R

I

V

RI

V^

E F F B F

BE CC

C

R

R

V

V

I

⎛^ ⎜⎜⎝

ELEC 301

BJT Bias Circuits

2

BJT Bias Configuration

Base-Emitter Loop

Collector-Emitter Loop

Fixed Bias w/ Collector Feedback npn

R^ B

R^ C I^ B^

I^ C + VCE- +VCC +V - BE^

I^ CC

I^ CC^

=^ I^ C

+^ I

B

(^

BE B F C F F C

BE BB C B C

BE BB C CC CC

V

R

R

I

V

RI

R

I

I

V

RI

R

I

V

⎤^ +⎥ ⎦

⎡^ ⎢ ⎣

⎛^ ⎜⎜⎝

β^ β

B F C

BE CC F F C^

R

R

V

V

I

β

β β

(^

CE CC

F F

CE C B C

CE C CC CC

V

VR RI

I

I

V

R

I

V

⎛^ ⎜⎜⎝

β^ β

C F F C CC CE^

R

I

V

V^

⎛^ ⎜⎜⎝

β^ β

Fixed Bias wi/ Emitter and Collector Feedback npn

R^ B

R^ C I^ B^

I^ C + VCE- +VCC +V - BE^

I^ CC R^ E

I^ EE

I^ CC^

= I^ C

+ I

B

(^

(^

)^

⎡^ ⎢ ⎣

⎛^ ⎜⎜⎝

B F E C F F C BE

E EE BE BB C B C

E EE BE BB C CC CC

R

R

R

I

V

R

I

V

RI

R

I

I

R

I

V

RI

R

I

V

β^ β

B F E C

BE CC

F F C^

R

R

R

V

V

I

(^

)^

CE E C F F C

E EE CE C CC CC

V

R

R

I

R I V R I V

⎛^ ⎜⎜⎝

β^ β

(^

) E

C F F C CC CE^

R

R

I

V

V^

⎛^ ⎜⎜⎝

β^ β

ELEC 301

BJT Bias Circuits

4

BJT Bias Configuration

Base-Emitter Loop

Collector-Emitter Loop

Self Bias Equivalent Circuit

R R B C I^ B

I^ C + VCE- V^ BE^ +- R^ E^

I^ EE +VCC

= -I^ E

R^ B V^ BBR B V^ = _____________ CC

R^ B R^ B^

R^ =B +VCC

V^ BBR^ B V^ = _____________ CCR

B R^ +B^

R^ B R^ B R^ =B

R^ B1 R^ B Circuit at base of the BJT.

Thevenin equivalent of the circuit at the base of the BJ

⎛^ ⎜⎜⎝

E F F B F C BE

E EE BE BB BB

R

R

I

V

R

I

V

RI

V

β^ β

⎛^ ⎜⎜⎝

E F F C C CC

E EE CC CC CE

R

R

I

V

R

I

RI

V

V

β^ β

(^

)(^

) 1

1

1

1

1

2 1

2 2 1 1

2

⎞⎟⎟⎠

⎛^ ⎜⎜⎝

⎞⎟⎟⎠ ⎛⎜⎜⎝

=

− + ⎞⎟⎟⎠ ⎛⎜⎜⎝

=

⎞⎟⎟⎠ ⎛^ ⎜⎜⎝

=

F B B

B B

E

BE B B

B CC

F F

B F E

BE BB F F

E F F B F

BE BB C

R R

R R

R

V R R

R R V R

V V

R

R

V V I

β

β β

β

β β

β β β

Fixed Bias w/ Collector Feedback pnp

R^ B

R^ C I B

I^ C - VEC+ -V^ CC

  • V EB

I^ CC

C CC BB EB CC^

R

I

RI

V

V^

where

C B CC^

I

I

I^

and

BF C^

I

I

C CC CC EC^

R

I

V

V^

C F F C CC EC^

R

I

V

V^

⎛^ ⎜⎜⎝

β^ β

ELEC 301

BJT Bias Circuits

5

BJT Bias Configuration

Base-Emitter Loop

Collector-Emitter Loop

Self Bias Circuit pnp

Thevenin Equivalent Voltage:

2 1

(^2) B B

B CC BB^

R

R

R

V

V^

B F E

BB EB F F C^

R

R

V

V

I

β

β β

2 1

2 1

B B

B B B^

R

R

R

R

R^

CC EC EC

F F

CC EC EE

CC

RI

V

RI

RI

V

RI

V

⎛^ ⎜⎜⎝

β^ β

C

E C F F CC EC C^

I

RI

V V R

⎞⎟ ⎟⎠ ⎛^ ⎜⎜⎝

− − =

β^ β

1

Bias StabilityA set of three stability factors is used to quantify the variation in the collector current with respect to the reverse saturation current,base-emitter voltage, and

βF^

.^ The stability factors are:

C^ F C F

C BE C BE V C CO C CO I

I

I

S

I V

I V

S

I I

I I

S

β^

=^

,^

.^

The stability of the bias configuration is quantified with respect to the collector current for the following reasons:

-^

the collector current is dependent on the base current and the collector-emitter voltage, and determines the output signal ofa BJT amplifier,

-^

small variations in

β, F^

I^ CO

, and

Δ V

can result in a large change in BE

I^ C^

The total incremental change in I

for small changes inC

I^ CO

,^ V

, and BE

β F^

is,

Δ I^ CT

=^ S

Δ II

+ CO^

SV^

Δ VBE

+^ S

F^

.^

Equation (3.7-7) clearly shows that in order to keep the change in I

small, the magnitude of the stability factors must also be keptC^

R small. B

R C I B

I C -V - + R E CC I

E

R B

  • VEC+ V^ EB