Of course, things don’t work that way-quite the opposite, actually-as the PNP and NPN sensor designation refers to the type of transistor (or equivalent for more involved devices-some can even be wired in either configuration) used inside of it. If you learned to use sensors before gaining an understanding of transistors themselves, it would be easy to think that a PNP transistor is controlled with positive voltage. PNP sensors produce a positive output to your industrial controls input, while NPN sensors produce a negative signal during an “on” state. As they are normally referred, PNP and NPN sensors are both supplied with positive and negative power leads, then produce a signal to indicate an “on” state. If you’re just learning about these components, industrial sensors can throw another wrench into one’s understanding of the concept if you’re not careful. When designing a circuit, it’s extremely helpful to have this second type of switching option available. One such application is a class B amplifier, where a matched pair of PNP and NPN transistors work in tandem in order to efficiently amplify oscillating signals. There are, however, certain circuits that benefit from PNP-type transistors, that would be difficult if not impossible to implement without this second type of transistor. Adding on to this advantage is the fact that NPN transistors are also easier, and thus cheaper, to manufacture than PNP transistors. This presents a huge advantage in high-speed switching and amplifier circuits applications. This is due to the fact that the “N” substrate can transfer electrons significantly faster than “P” type substrates can transport positive electron holes. There are, in fact, some differences, and in most circuit design applications NPN transistors are preferred. While PNP and NPN sensors do the same basic job, you might wonder why one would be used over another. Whereas in a PNP configuration, the load is wired between the collector and ground. Also, the load you’re controlling is wired between a positive voltage and the controlling transistor’s collector in an NPN configuration. PNP transistors (sometimes called 'sourcing sensors') performs the same job, but is set up so that a negative voltage must be applied to the base pin to allow current to flow from the emitter to the collector lead. Above a certain point a transistor reaches saturation, allowing electrons to flow freely.

This proportional current flow occurs in an active range, but below a certain cutoff voltage no current flows. NPNsįrom a practical standpoint, NPN transistors (sometimes called 'sinking sensors') amplify a positive signal applied to the base by allowing a larger current to flow from the collector to emitter pins of the device, proportional to the base voltage. While both have the ability to amplify signals or even act to switch larger currents on and off, they accomplish this signal boosting ability in different ways.

Difference Between NPN and PNPs Transistors

Pnp npn transistor symbol