On the other hand, removing the control signal will turn off the power transistor. For instance, the supply of input current to the base terminal switches it on. Nonetheless, for the power transistor, you’ll find unique controlled characteristics. While its structure is different from other transistors, it operates under the same principle.
Primarily, it is a junction transistor, but you can regard it as a semiconductor field-effect transistor. You’ll find this transistor in power supplies systems and high-power amplifiers. It is a transistor type that is key in switching and amplifying electronic signals and electrical power. What is the Power Transistor?įig 1: An Electronics Engineer Working on a Circuit Board In addition, it’ll explain the operational principle, pros, and cons, among other key insights. Nonetheless, the emphasis will be on the power transistors for this guide. Here is where a power transistor comes in handy.Īt OurPCB, we have all the key insights on any type of transistor. Such a unit requires power amplifiers to deliver just the right amount of current. The key wires to take note of are solid red, black and blue wires.Think of a power supply system that delivers high power levels. NOTE the dotted line in the following diagram is optional and may or may not be required, depending on your hardware/setup. Many modern PLC input cards can be configured and wired to be either 'sinking' or 'sourcing' although it will usually necessitate all inputs on a particular input card being configured the same. Less common nowadays are input cards that 'source', these were popular in Asia and require the NPN type of sensor in order to operate correctly. Most common in Europe is the 'sinking' type of input, these will be used with the PNP sensor as shown below. It is worth mentioning, that whilst the terms sinking / sourcing and positive / negative logic are well known in some industries, they are not always commonly used terms. It is therefore important to identify the type of sensor to be used with the PLC card based on the PLC manufacturer's documentation and / or wiring diagrams. Two types of input cards exist, those that 'sink' current (also known as positive logic) and those that 'source' current (also known as negative logic). When selecting a sensor to be used with a PLC, it is very important that the sensor matches the type of PLC input card to be used. Use with a programmable logic controller (PLC). PNP sensors tend to be more commonly used. When used in a traditional relay type control circuit, it is normally possible to use either the PNP or the NPN type of sensor as shown below. The selection of a PNP sensor verses an NPN sensor is determined by the nature of the circuit the device is to be used in. Further learning material regarding PNP and NPN transistors can be found online from several sources. However, for ease of understanding please see attached a page extracted from our Practical Aspects book, showing (in brief) transistor terminology and circuit diagrams.
Please note that the subject of this FAQ is specifically related to wiring PNP/NPN outputs for sensors, not to give a detailed understanding of transistor technology. a PNP sensor may be either N/O or N/C as can an NPN be either N/O or N/C. Refer to attached document for simple explanation of the two.Ī key point to observe is that PNP and NPN has nothing to do with whether the sensor is normally open (N/O) or normally closed (N/C), i.e.
The difference is a result of the internal circuit design and type of transistors used. Two specific types of 3 wire sensors are available PNP and NPN. Solid state electronic components such as transistors are used to switch the output of the sensor upon detection of an object.
The term solid state refers to the type of components used within the sensor. Most industrial proximity sensors (inductive, capacitive, ultrasonic and photo electric) are solid state.
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