PNP Sensor Vs NPN Sensor Wiring Explanation
Bipolar Junction Transistors come in two different flavors: NPN and PNP. These abbreviations note that they’re formed with either a positively-doped semiconducting material sandwiched between two negatively-doped materials in the case of an NPN transistor, or a negatively doped material sandwiched between two positive layers in the case of PNP devices.
Difference Between NPN and PNPs Transistors
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.
NPNs
From 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. This proportional current flow occurs in an active range, but below a certain cutoff voltage no current flows. Above a certain point a transistor reaches saturation, allowing electrons to flow freely.
PNPs
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. Also, the load you’re controlling is wired between a positive voltage and the controlling transistor’s collector in an NPN configuration. Whereas in a PNP configuration, the load is wired between the collector and ground.