![]() A PNP sensor (also called a sourcing sensor) sources positive power to the transistor's output. Both types of sensor have positive and negative power leads, but the PNP type produces a positive output in the ON state while the NPN type signal in the ON state is negative. ![]() So What's The Difference?īoth types of transistor can amplify signals and switch larger currents, but they do it in different ways. The device the sensor is connected to is the load, which might be anything from a relay or PLC input to a lamp or a pneumatic valve. In the most basic terms, P=Positive and N=Negative. The semiconducting material of which they're constructed is either a positive layer situated between two negative layers (NPN), or a negative layer between two positive layers (PNP). ![]() PNP and NPN are types of bipolar junction transistor, with the two different abbreviations denoting their composition. However, this designation just indicates the type of transistor used inside the device. When dealing with electronic connections, for example to a PLC, people usually refer to PNP or NPN sensors. For example, to put an NPN into saturation mode, VB should be higher than VC and VE.Most industries these days use solid-state sensors in their electronic devices, meaning that they use solid semiconducting components like transistors to switch the sensor's output when it detects something. PNPs and NPNs work pretty much alike, but their modes are different because of the current polarities. NPN transistors require a power supply with positive polarity with respect to common terminals, but PNP transistors require a negative power supply. It is clear that the current directions and voltage polarities in PNPs and NPNs are always opposite to each other. The NPN transistor always has an arrow pointing out. The arrow shows the direction of the current and how it is always on the emitter In a PNP transistor, however, the current flows from the emitter to the collector ( Figure. In an NPN transistor, the current flows from the collector (C) to the Emitter (E) ( Figure. In a PNP transistor, a positive voltage is given to the emitter terminal to produce current flow from the emitter to collector. In an NPN transistor, a positive voltage is given to the collector terminal to produce a current flow from the collector to the emitter. Reverse Active: Like active mode, the current is proportional to the base current, but flows in reverse.The transistor appears as a near short circuit between the collector and emitter terminals. Saturation: BJT operates in this zone in switching operations.Active: BJT operates in this zone for amplifier circuits because the transistor can act as a fairly linear amplifier.Cutoff: BJT operates in this zone in switching operations.BJTs can operate in different modes depending on the junction biasĪ PNP transistor has a layer of N-doped semiconductor between two layers of P-doped material (Courtesy of Wikibooks)Īn NPN transistor has a layer of P-doped semiconductor between two N-doped layers (Courtesy of Wikibooks) The junctions between N and P regions are similar to the junctions in diodes and they can be forward-biased or reverse-biased as well. 2) while the NPN transistor has one P region between two N regions ( Figure. The PNP transistor has one N region between two P regions ( Figure. The semiconductor physics of BJTs will not be discussed here, but it is worth mentioning that a BJT is fabricated with three separately doped regions with two junctions. The transistor symbol indicates the three terminals. The Base is responsible for controlling the transistor while the Collector is the positive lead, and Emitter is the negative lead. A transistor is an active device with three terminals, and these three terminals are known as the Emitter (E), the Base (B), and the Collector (C) (Figure. BJTs are made of doped materials and can be configured as NPN and PNP. There are two main types of transistor: bipolar junction transistors (BJTs) and field effect transistors (FETs). Here, we focus specifically on bipolar junction transistors. Millions of transistors are found in integrated circuits across every electronic device.
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