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. PNP Proximity Sensor Output goes HIGH when metal object is near it.Difference Between NPN and PNPs Transistors PNP Proximity Sensor Output is normally LOW when nothing is near it. NPN Proximity Sensor Output goes LOW when metal object is near it. NPN Proximity Sensor Output is normally HIGH when nothing is near it. Whether to use NPN or PNP depends on which direction you want the current to flow.Ī NPN sensor sinks current to drive the ED input to 0V.Ī PNP sensor sources current to drive the ED input to a positive voltage.Īn example of an NPN and PNP sensor is shown below: A NPN Sensor
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