Switching functions

Some switching functions are: PNP, NPN, SPST and SPDT.
PNP and NPN are bipolar junction transistors (BJTs). BJTs are made of doped materials and provide amplification or switching capability. It’s easy to remember that NPN stands for Negative-Positive-

Negative and PNP stands for Positive-Negative-Positive transistors. Briefly, the NPN transistor requires positive current from the base to the emitter and PNP requires negative current to the base, but current must flow out from the base to ground.

A Single Pole Double Throw (SPDT) switch is a switch that only has a single input and can connect to and switch between the 2 outputs. This means it has one input terminal and two output terminals.

A Single Pole Double Throw switch can serve a variety of functions in a circuit. It can serve as an on-off switch, depending on how the circuit is wired. Or it can serve to connect circuits to any 2 various paths that a circuit may need to function in. For example, a SPDT switch can connect to create a Ready Mode and a Standby Mode in a printer.