1.9 KiB
There are two types of transistors:
Bipolar Junctions Transistors (BJT)
The current flowing in from Base controls the much larger current flowing between Collector and Emitter.
Rules for NPN Transistors
1. Polarity The collector must be more positive than the emitter.
2. Junctions The base$\rightarrow$emitter and base$\rightarrow$collector connections behave like diodes.
3. Maximum Ratings
Any transistor has maximum ratings for I_C ,$I_B$ and V_{CE} that should not be exceded.
4. Current Amplifier
When rules 1-3 are obeyed, I_C is roughly equivalent to IB and can be written like:
\displaystyle I_C = \beta I_B
In the following example circuit we can see that for a \beta of 100 the Ic current is aroung 100 times higher than the base current.
$ 1 0.000005 11.086722712598126 50 5 43 5e-11
R 256 16 256 -48 0 0 40 2 0 0 0.5
g 256 144 256 208 0 0
t 192 80 256 80 0 1 -1.552 0.44799999999999995 100 default
R 144 80 64 80 0 0 40 0.44799999999999995 0 0 0.5
w 256 16 256 64 3
w 256 96 256 144 3
w 144 80 192 80 1
x 272 -5 289 -2 4 24 C
x 273 179 289 182 4 24 E
x 96 68 112 71 4 24 B
x 266 82 275 85 4 12 Ic
o 1 16 0 159745 0.0001 0.0001 0 2 1 3
38 3 F1 0 0 1.4 -1 Voltage
NPN vs PNP Transistors
The names come from the way they are constructed
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Transistor Modes
Saturation
In this mode the transistor acts like a short circuit and current flows freely from emitter to collector.
Cut-Off
In this mode the transistor acts like an open circuit and no current flows from emitter to collector.
When V_C > V _B < V_E then the transistor acts in Cutoff Region
Active
The current from collector to emitter is proportional to the current flowing into the base.