Programming instructions

 National Instruments Corporation 4-1 Multisim Component Reference Guide
Chapter 4
Transistors
4.1 BJT (NPN & PNP)
A bipolar junction transistor, or BJT, is a current-based valve used for controlling electronic
current. BJTs are operated in three different modes, depending on which element is common
to input and output: common base, common emitter or common collector. The three modes
have different input and output impedances and different current gains, offering individual
advantages to a designer.
A transistor can be operated in its nonlinear region as a current/voltage amplifier or as an
electronic switch in cutoff and saturation modes. In its linear region, it must be biased
appropriately (i.e., subjected to external voltages to produce a desired collector current) to
establish a proper DC operating point. The transistors' parameters are based on the Gummel-
Poon transistor model.
BJTs are commonly used in amplification and switching applications. They come in two
versions: NPN and PNP. The letters refer to the polarities, positive or negative, of the
materials that make up the transistor sandwich. For both NPNs and PNPs, the terminal with
the arrowhead represents the emitter.
An NPN transistor has two n-regions (collector and emitter) separated by a p-region (base).
The terminal with the arrowhead is the emitter. The ideal NPN in the parts bin has generic
values suitable for most circuits. You can specify a real-world transistor by double-clicking
the icon and choosing another model.
A PNP transistor has two p-regions (collector and emitter) separated by an n-region (base).
The terminal with the arrowhead represents the emitter. The ideal PNP model has generic
values suitable for most circuits. You can specify a real-world transistor by double-clicking
the icon and choosing another model.
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