Embedded Systems Transistors

heartlustElectronics - Devices

Nov 2, 2013 (3 years and 11 months ago)

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Laboratory for Perceptual Robotics


Department of Computer Science

Embedded Systems

Transistors

Laboratory for Perceptual Robotics


Department of Computer Science

Bipolar Transistor

B

E

C

NPN

C

B

E

C

PNP

P

N

N

E

B

NPN rules:

1.
The collector must be more positive than the emitter

2.
B
-
E and B
-
C behave like diodes


B
-
E forward biased


B
-
C reverse biased

3.
Limitations on I
C
, I
B
, and V
CE

4.
When rules (1)
-
(3) are obeyed,

I
C
=h
FE
I
B
=

I
B

h
FE
(current gain) ~ 100

i
C

governed by

transistor action

Laboratory for Perceptual Robotics


Department of Computer Science

Bipolar Transistor

P

N

N

E

B

C

+

+

small I
C

large I
CE

Laboratory for Perceptual Robotics


Department of Computer Science

Transistor Action

P

N

N

E

B

C

B

E

C

I
C
=

I
B

reverse biased

forward biased

Laboratory for Perceptual Robotics


Department of Computer Science

Transistor Saturation

switch closes:


V
BE
=0.6V


lamp

0.1A

10 V

1K


C

B

E

10 V

I
B
=9.4V/1K

=9.4mA

I
CE
=

(I
B
)=100(9.4)


=940mA

to get that much current through the lamp V
C

would have to go
significantly below ground, which is illegal by rule #1


“The collector must be more positive than the emitter”


the transistor is saturated
---
only enough I
C

current

flows through the
transistor to keep the collector 0.05 to 0.2 V more positive than the
emitter.

Laboratory for Perceptual Robotics


Department of Computer Science

Emitter
-
Follower

V
in

V
out

V
E

= V
B
-
0.6V

when Vin > 0.6V




big current/power gain at

Vout=Vin
-
0.6V




impedance buffer

Laboratory for Perceptual Robotics


Department of Computer Science

Power Transistors



Darlington pairs




h
FE
=(h
FE
)
2




TIP102/106

Laboratory for Perceptual Robotics


Department of Computer Science

Push
-
Pull Amplifier Stages

NPN can only “source” current

PNP can only “sink” current

“crossover”

distortion