Figure 10 shows a circuit for a common NPN-transistor that connects to an LED. The transistor base connection controls the amount of current that flows. Schematic-diagram symbols for an NPN and a PNP transistor.īoth transistor types operate as current devices, so think of them as valves for current flow. The arrow’s direction identifies the transistor type in data sheets and schematic diagrams.įigure 9. The arrow points out for an NPN transistor and in for a PNP transistor. In circuit diagrams, the emitter always appears as an arrow.
NPN and PNP transistors each have three leads, a collector, a base, and an emitter, as shown in Figure 9. Before discussing sensors and controller outputs, a short explanation of both transistor types will get you off to a good start without the need for a degree in semiconductor physics! (The Ps and Ns refer to types of semiconductor material.) PNP?Ī: The initials indicate a type of transistor used in the output section of many sensors. What do these abbreviations mean and what are the differences between NPN vs. Some of the sensors I plan to use come in two varieties, PNP and NPN. Q: Now I understand relays and current sinks and sources. In the first two installments, Jon covered relays and sink vs. In the third installment of this five-part series, Jon Titus explores the basic elements of a control system.
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