How do you distinguish between PNP and NPN in transistor application circuits?

How does the transistor work and what is the important role in it?

Triode, the full name should be semiconductor transistor, also known as bipolar transistor, transistor, is a kind of semiconductor device that controls the current current, its function is to amplify the weak signal into an electrical signal with a large amplitude value, and is also used as a contactless switch. Common transistors are 9012, 8550, 9013, and 8050. The main role of the transistor in the single-chip microcomputer application circuit is the switching function. Among them, 9012 and 8550 are PNP transistors, which can be used universally. Among them, 9013 and 8050 are NPN type transistors, which can be used universally. There are two types of transistor structures: NPN and PNP, because electrons have higher mobility than holes, so NPN is more widely used than PNP transistor.

How to distinguish between NPN and PNP

(1) NPN is to control the current (IC) of C→E with the current (IB) of B→E, the E pole potential is the lowest, and the C pole potential is usually the highest when normal amplification, that is, VC>VB>VE

PNP uses the current (IB) of E→B to control the current (IC) of E→C, the E pole potential is the highest, and the C pole potential is usually the lowest when normal amplification, that is, VC

(2) In the NPN circuit, E is ultimately connected to the floor (directly or indirectly), and C is ultimately connected to the ceiling (directly or indirectly). The PNP circuit is the opposite, where C is ultimately connected to the floor (directly or indirectly) and E is ultimately connected to the ceiling (directly or indirectly). This is also to satisfy the relationship between VC and VE above.

(3) NPN base high voltage, collector and emitter short circuit. Low voltage, open collector and emitter. That is, not working.

The base of PNP is high-voltage, and the collector and emitter are open-circuited, that is, it does not work. If the base is underpowered, the collector is short-circuited to the emitter.

(4) The difference between NPN and PNP transistor:

a) If the input is high and the output needs to be low, NPN is selected first.

b) If the input level is low and the output level needs to be low, PNP is selected first.

c) If the input is low and the output needs to be high, NPN is selected first.

d) If the input level is high and the output level needs to be high, PNP transistor is selected first.