Contents
How can a PNP transistor be used as a switch?
For a PNP transistor, the Emitter potential must be positive with respect to the Base. Then the transistor operates as a “single-pole single-throw” (SPST) solid state switch. With a zero signal applied to the Base of the transistor it turns “OFF” acting like an open switch and zero collector current flows.
Why we use NPN not PNP?
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. mobility of electrons is more than hole,so as a result npn transistor are faster than pnp that’s why they are preferred..
How can you tell NPN from PNP?
An NPN transistor has a piece of P-type silicon (the base) sandwiched between two pieces of N-type (the collector and emitter). In a PNP transistor, the type of the layers are reversed. Below is a typical cross section of a transistor. NPN and PNP transistors have very similar schematic symbols.
How is a NPN input connected to a PNP sensor?
An NPN input is looking for the input to be connected to GND to respond. If connected to a PNP sensor, the NPN input will be floating (open) when the PNP sensor is off (not triggered).
When does the PNP connect to the NPN?
This current flow might be high enough to falsely trigger the NPN input. When the PNP sensor turns on, it will connect +24VDC to the NPN input.
Can a pull down resistor be used to convert PNP to NPN?
Alternatively, a pull-down resistor can be used to convert from PNP to NPN. For dc sensors, in addition to NPN or PNP, you might also come across two-wire sensors, which could be wired into a PNP or NPN input in either configuration.
How to decide between PNP and NPN-control design?
Historically, Asia standardized early on NPN sensors, while in Europe the popular choice is PNP. Generally speaking, the sourcing sensor and sinking input terminology is correct. However, some manufacturers will label an input for the corresponding output device, rather than the actual function of the input itself.