What is PNP and NPN junction?
NPN and PNP transistors are bipolar junction transistors, and it is a basic electrical and electronic component which is used to build many electrical and electronic projects. The main difference between the NPN and PNP transistor is, an NPN transistor turns on when the current flows through the base of the transistor.
A PNP works in a same but opposite fashion. The base still controls current flow, but that current flows in the opposite direction – from emitter to collector. Instead of electrons, the emitter emits “holes” (a conceptual absence of electrons) which are collected by the collector.
- The pnp transistor works essentially the same as the npn transistor. However, since the emitter, base, and collector in the pnp transistor are made of materials that are different from those used in the npn transistor, different current carriers flow in the pnp unit.
- The DC load line is the load line of the DC equivalent circuit, defined by reducing the reactive components to zero (replacing capacitors by open circuits and inductors by short circuits). It is used to determine the correct DC operating point, often called the Q point.
- A PNP works in a same but opposite fashion. The base still controls current flow, but that current flows in the opposite direction – from emitter to collector. Instead of electrons, the emitter emits “holes” (a conceptual absence of electrons) which are collected by the collector.
PNP sensors are sometimes called “sourcing sensors” because they source positive power to the output. NPN sensors are sometime called “sinking sensors” because they sink ground to the output. The term “load” identifies the device the sensor powers. The load could be a lamp, pneumatic valve, relay or PLC input.
- PNP and NPN sensors are 3 wire DC devices. The difference is in the type of transistor used in the sensor. The PNP device has 2 control power leads, one connected to positive, the other to negative. However, on an NPN device, the remaining lead from the load must be connected to the positive pole of the power supply.
- The outputs of some sensors will behave like transistors, when a sensor senses an object it will trigger the transistor controlling the output (which essentially acts like a switch) and depending on its design it'll act as an NPN or PNP type transistor. An NPN output is commonly called a “sinking” output.
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The main difference between the two types of transistors is that holes are the more important carriers for PNP transistors, whereas electrons are the important carriers for NPN transistors. Then, PNP transistors use a small base current and a negative base voltage to control a much larger emitter-collector current.
- One of the most common uses for transistors in an electronic circuit is as simple switches. In short, a transistor conducts current across the collector-emitter path only when a voltage is applied to the base. When no base voltage is present, the switch is off. When base voltage is present, the switch is on.
- As mobility of electrons are greater than holes. A NPN transistor has electrons as majority charge carriers whereas the PNP transistor has holes as majority charge carrier. The mobility of electrons is better than mobility of holes. So a NPN transistor is faster in operation than a PNP transistor.
- A transistor is a miniature electronic component that can do two different jobs. It can work either as an amplifier or a switch: When it works as an amplifier, it takes in a tiny electric current at one end (an input current) and produces a much bigger electric current (an output current) at the other.
Updated: 12th November 2019