In a nutshell, the NPN transistor needs a specific current from the base to the emitter, while the PNP transistor requires a negative current from the base to the emitter, but both require current to flow out of the base to the ground. It identifies this as a logic HIGH signal when linked to a PLC input. When an object reaches the sensor’s detection range, the sensor’s output is linked to +24V. PNP SensorsĪs they source positive power to the output, PNP sensors are also referred to as “sourcing sensors.” The active high output is provided by PNP proximity sensors. Either the load is linked to negative with the positive switch (PNP), or the load is coupled to positive with the negative switch (NPN). The term “switched” refers to the electrically switched side of the controlled load (relay, tiny indicator, or PLC input). PNP switch stands for ‘Switched Positive’. Due to holes, the Collector current (IC) travels through the Collector-Base area. The remaining holes will proceed to the Collector if they do not merge with electrons in the Base. The majority of charge carriers in the Emitter current flow through the holes. The current will flow via the Emitter-Base connection due to the movement of holes. As a result, nearly all Emitter holes will cross the depletion area and penetrate the Base layer. Simultaneously, a small number of electrons from the base enter the Emitter and merge with the holes.Īs the Base is a very lightly doped and narrow region, the number of electrons in it is quite small. As a result, several holes from the emitter pass the depletion region and reach the Base. The junction between the emitter and the base is forward-biased. PNP Transistor: How Does it Work? (Symbol & Working Principle) | Electrical4U Working Principle
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