PNP and NPN transistor switching circuits

Transistors are most commonly used in switching circuits. The following introduces PNP type and NPN type transistors respectively. Let’s talk about PNP transistors first. Commonly used models include 9012, 8550, etc. How to use it, as shown below:

FM is a buzzer, 8550 is a PNP transistor, terminal C is connected to ground, terminal B is controlled by the microcontroller, and terminal E is connected to VCC through FM. According to the direction of the arrow, when terminal E is at high voltage, when terminal B is also at high voltage, then E and C are disconnected. When terminal B is at low voltage, then E and C are directly connected to realize the switch function. Simple trick: If the diode is in the direction of the arrow on the triode, as long as the diode is forward-conducting, the triode will conduct up and down.

The same is true for NPN transistors, so I won’t explain too much here.

It can be seen here that when a triode is used as a switching tube, it is very simple and does not involve any so-called formulas, magnification calculations, etc.