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Transistor
Tutorial Transistor Terminology A transistor has three legs: a collector, an emitter and a base. Below is the symbols for an NPN and a PNP transistor.
NPN transistor
PNP transistor
Transistors as switches The easiest way to understand transistors is to think of them as switches. You can switch a big current (between the collector and emitter) with a much smaller current (in the base). Lets look at an example:
NPN transistor as a switch (on)
NPN transistor as a switch (off) The
circuit above is a typical example of driving LED's from a microcontroller or
a PC's parallel port. The port is well protected because it will only supply a
small current, though the small current is enough to switch a much bigger load.
A PNP transistor works the same as an NPN transistor, except the current flows from the base, not into the base..
PNP transistor as a switch (on)
PNP transistor as a switch (off) Also note that the emitter is always tied to the fixed voltage (+12V or GND) when using transistors as switches. In the following tutorials (coming soon) we will show you how to do calculations with transistors.
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(c) 2010 Mayothi |
